Plant Kingdom

The following is an estimate of the known species of plants on the globe at different dates:—

   Phanerogams.  Cryptogams. Total.
According to Linnæus,1753,5,323   615  5,938
Pusoon,1807,19,949   6,000  25,949
Stendel,1824,39,684   10,765  50,649
Stendel,1841,78,000   13,000  91,000
Stendel,1844,80,000   15,000  95,000

The advance made of late years in the knowledge of existing species will be apparent from a consideration of Lindley's estimate in 1846:—

 Genera. Species.
Thallogens,   939  8,394
Acrogens,310  4,086
Rhizogens,21  53
Endogens,1,420  13,684
Dictyogens,17  268
Gymnogens,37  210
Exogens,6,191  16,225
   ——————
      Total,8,935  92,920

Herbaceous Plants which best endure the cold of Winter.

The "way to look at things," which is the true foundation of science, varies, not only according to a man's degree of intellectual cultivation, but according to his social condition or profession. The herborist has eyes only for the plants in which he deals,—the "simples" which, as we read in old Gerarde, wrought such wonderful cures in the days of our forefathers,—and from the most exquisite flowers he turns with indifference. The gardener, on the other hand, is wholly absorbed by his love and his hate,—his charming exotics, and his troublesome weeds. The latter he regards with much the same feelings as a society wholly composed of honest men would regard an infusion of the "dangerous elements;" for weeds, like rogues, take what is not their own, and deprive others of their means of sustenance. But to classify plants according to their virtues or vices is not worthy of science, exclaims the rigid botanist. Would you mingle vile self-interest with the pure study of the vegetable kingdom? Remember that all selfish feelings ought to be banished from the sublime sanctuary of analysis and synthesis.

This sounds exceedingly well. Disinterested words, from whatever quarter they come, always produce—perhaps, on account of their comparative rarity—an admirable effect. But what is their real value? To ascertain it, the listener must be able to seize, like so many luminous threads, all the emotions which are acting upon the heart and tongue of the speaker. But we are very far from having arrived at this degree of perfection. Shall we ever attain to it? Yes, because we can conceive its possibility. But, until that golden epoch, the pure love of science will always remain a myth, and we shall not have universally understood the necessity of seeking in the profound study of nature the grand destiny of man.

It is among the weeds and noxious plants that we shall find the species capable of enduring longest the cold ofwinter. What part, then, do they fulfil in the economy of creation? An ambitious, but not a novel question, which has often been propounded in reference to our parasitical insects.

The best answer which we can make to it is this: Everything invites us to work. Labour is imposed even upon him who least desires it. Earth will yield a return only in proportion to the care we bestow upon her.

If, after having toiled and sown, we had nothing to do but to gather in the harvest, every person would become an agriculturist. But a soil which is not manured will soon grow exhausted; and if it be neither ploughed nor harrowed, instead of barley or vegetables, it will soon be covered with tares; rank weeds will flourish in every field. Such is the chastisement reserved for sloth,—the true "original sin" of the human race.

Well, then, it is among the weeds, everywhere so common, that we meet with the plants best able to brave the rigours of frost.

Causes of the Circulation of the Sap.

Let us return to the sap, the life-blood of vegetation.

How is it that its movement does not recommence at the same time in all plants? Why are some clothed with leaves when the others are scarcely budding? Wherefore, in certain genera, do the flowers appear before the leaves?

Some authorities assert,—but facts show it to be a purely gratuitous supposition,—that the flower, which, with the fruit, seems to be the goal or object of vegetation, demands a greater activity on the part of the sap. But, in truth, many trees and shrubs, such as the poplar, the willow, and the hazel, flourish at an epoch when the sap is barely aroused from its protracted lethargy.

These are questions which have still to be answered.

But upon yet another question we may dwell at some detail. What is the cause of the circulation of the sap?

To the best of our knowledge, this important problem has never been propounded as it should have been. And for this reason: all observers who have taken up its consideration have had in view only the rising sap , and the cause of its rising. Evidently this is but a part  of the problem. The ascending sap, after undergoing an important modification in the leaves, becomes the descending  sap; just as the venous blood is transformed, on coming into contact with the air in the lungs, into arterial blood. It is this alternative movement of going and coming which constitutes the circulation both of the sap and the blood, and which ceases completely only with the life of the plant or the animal. We must, therefore, bear in mind,—which has not been hitherto done,—these two opposite, yet indissolubly connected, movements, before we can approach with advantage the solution of the proposed question.[40]

Science consists in discovering, among the different ways of looking at things which present themselves to the mind, the one which appears to explain most clearly the phenomena submitted to observation. He who doubts the accuracy of our remark need only join us in reviewing the different opinions enunciated up to the present time on the cause of the rise of the sap.

Grew, an English botanist, a contemporary of Newton, and his fellow-member in the Royal Society of London, attributed the rise of the sap to the play of the utricles of which the plant is composed. These utricles, he said, maintain a close intercommunication; through their contraction, the sap passes from the lower to the upper, and thus arrives almost at the top of the plant. Grew's authority carried conviction to the minds of many botanists, particularly to those of his compatriots. Yet was his opinion altogether imaginary; the supposed contraction of the utricles does not exist.

La Hire, a French botanist, who flourished at the beginning of the eighteenth century,—son of the geometrician of the same name,—pretended that he could account for the rise of the sap by the play of the little valves with which the interior of the sap-vessels was furnished; at the same time he assigned a very active rôle  to the fibres of the roots. The fibres elevate, he said, the whole column of superimposed liquid, incessantly introducing, by a kind of suction, new fluids into the organs.

Unfortunately, the "play of the little valves, with which the interior of the sap-vessels is furnished," is a pure invention of La Hire's. Instead of growing wise by experiment, he suffered himself to be led astray by a false analogy. Valves are found in the veins of man and the mammals; but no one has ever seen the sides of the vessels of a plant garnished with valves to induce a circulation of the sap.

Mariotte, so well known by his researches into the compressibility of air, represented the rise of the sap as dependent upon what he called "the attraction taking place in the narrow tubes"—upon what, in fact, we now term capillarity . "This first entrance of water into the roots is in obedience," he said, "to a law of nature; for wherever very narrow tubes exist which touch the water, it enters into them, and even rises, contrary to its natural inclination."

Many botanists adopted the opinion of Mariotte. But if it were well founded, all capillary  bodies, even inorganic ones, ought to present a circulatory movement analogous to that of the sap. Now, this is not the case. A body must be animated, must be living, for attraction to take place in the narrow tubes, and to produce a movement comparable to that of the nutritive liquid.

Malpighi attributed the rise of the sap to the alternating rarefaction and condensation of this liquid by heat; Perrault, to a kind of fermentation; De Saussure, to a peculiar irritability of the vessels. Of these three hypotheses, the first is purely physical; the second, chemical; the third, vital. So, as we see, there is something for everybody—chacun à son gout!

The same question has, in our own day, been taken up from a new point of view, on the occasion of Dutrochet'sdiscovery of the endosmose. This philosopher was one of the first to perceive that two liquids, separated from one another by a membrane, quickly effect or induce a current which always carries the thinner liquid towards the denser, and ends by mingling the two completely. "It is endosmose," he said, "which produces at one and the same time the progression of the sap by impulsion , and its progression by affluxion . The sap would receive its impulse in the spongioles of the roots; thence would be carried towards the upper parts by the turgescence of the organs—by the affluxion, which would thus act as a forcible mode of suction."

The basis of this theory is, that the sap contained in the upper parts will be more concentrated or denser than that in the lower portions of the same plant. But this is a mere supposition. And even this supposition has been swept away by the recent experiments of Hartig and others, which show that the difference in density between the two saps is not only almost null, but in many ligneous plants the lower sap is, on the contrary, denser than the upper.[41]

Finally, and more recently, M. Joseph Boehm has put forth a theory which offers some points of analogy with that of Grew. According to Boehm, the rise of the sap is the effect of a suction, the cause of which must be sought both in the atmospheric pressure and in the transpiration which takes place through the organs, and notably through the leaves of the plant. The part which he attributes to the cellules, of which the organs are composed, he thus describes:—"When the superficial cellules of the plant lose water by transpiration," he says, "of two things, one will happen: either these cellules will contract and shrivel, or they carry up, by a kind of aspiration, to the neighbouring cellules, situated in deeper layers, a quantity of water equivalent to what they had lost. In the normal condition, the latter is always the result; each cellule takes from its neighbour what itself has lost, and this action, becoming more and more general, is continued from the leaves to the extremities of the roots. The cellules of the spongioles replace the water which they have yielded, from the humid medium surrounding them."

In support of this theory,[42] M. Boehm has made several experiments, which, we fear, will not carry conviction to every mind.

In the different theories which we have been attempting to explain, their authors, as it seems to us, have neglected an essential element—the life  of the plant. Then, the experiments undertaken by way of proof, have been made upon cut stems or branches, which, consequently, did not enjoy their integral vitality. In fact, the results indicated could just as well have been obtained with inert as with living matter.

Taking into account all these considerations, we are doubtful whether any value can be placed on the theories just enunciated. Undoubtedly, physical causes, such as capillarity, heat, evaporation, atmospheric pressure, electricity, have a certain marked and constant action. But this action is here complex; it is found combined with a new force, whose effects constitute precisely the profound difference which exists between the massive mineral framework of the globe and the transitory beings peopling its surface. It matters little whether we call it vital force , or otherwise; sufficient that it exists . We must, therefore, allow for its influence when endeavouring to explain the varied movements of which plants, as well as animals, may be the seat.


[40]The best means of ascertaining the coexistence of an ascending and descending sap have been indicated in "The Circle of the Year," pp. 163-8.

[41]See the Botanische Zeitung  ("Botanical Gazette") for the years 1853, 1856, 1859, and 1861.

[42]Boehm, "Sur la Cause de l'Ascension de la Séve," Mémoire communiqué à l'Académie des Sciences de Vienne, juillet 1863.

The Changes Which Take Place in the Food of Plants During Their Growth

The simple compounds which the plant absorbs from the atmosphere and soil are elaborated within its system, and converted into the various complex substances of which its tissues are composed, by a series of changes, the details of which are still in some respects imperfectly known, although their general nature is sufficiently well understood. They may be best rendered intelligible by reference, in the first instance, to the changes occurring during germination, when the young plant is nourished by a supply of food stored up in the seed, in sufficient quantity to maintain its existence until the organs by which it is afterwards to draw its nutriment from the air and soil are sufficiently developed to serve that purpose.

Changes occurring during Germination.—When a seed is placed in the soil under favourable circumstances, it becomes the seat of an important and remarkable series of chemical changes, which result in the production of the young plant. Experiment and observation have shown that heat, moisture, and air, are necessary to the production of these changes, and though probably not absolutely essential, the absence of light is favourable in the early stages. The temperature required for germination variesgreatly in different seeds, some germinating readily at a few degrees above the freezing point, and others requiring a tolerably high temperature. The rapidity with which it takes place appears to increase with the temperature; but this is true only within very narrow limits, for beyond a certain point heat is injurious, and when it exceeds 120° or 130° Fahrenheit, entirely prevents the process. The presence of oxygen is also essential, for it has been shown that if seeds are placed in a soil exposed to an atmosphere deprived of that element, or if they be buried so deep that the air does not reach them, they may lie without change for an unlimited period; but so soon as they are exposed to the air, germination immediately commences. Illustrations of this fact are frequently observed where earth from a considerable depth has been thrown up to the surface, when it often becomes covered with plants not usually seen in the neighbourhood, which have sprung from buried seeds. When all the necessary conditions for germination are fulfilled, the seed absorbs moisture, swells up, and sends out a shoot which rises to the surface, and a radicle which descends—the one destined to develop the leaves, the other the roots, by which the plant is afterwards to derive its nutriment from the air and the soil. But until these organs are properly developed, the plant is dependent on the matters contained in the seed itself. These substances are mostly insoluble, but are brought into solution by the atmospheric oxygen acting upon the gluten, and converting it into a soluble substance called diastase, which in its turn reacts upon the starch, converting it first into dextrine, and then into cellulose, and the latter is finally deposited in the form of organised cells, and produces the first little shoot of the plant. At the first moment of germination, the oxygen absorbed appears simply to oxidize the constituents of the seed, but this condition exists only for a very limited period, and is soon followed by the evolution of carbonic acid, water being at the same time formed from the organic constituents of the seed, which gradually diminishes in weight. The amount of this diminution is different with different plants, but always considerable. Boussingault found that the loss of dry substance in the pea amounted in 26 days to 52 per cent, and in wheat to 57 per cent in 51 days. Against this, of course, is to be put the weight of the young plant produced; but this is never sufficient to counterbalance the diminished weight of the seed, for Saussure found that a horse bean and the plant produced from it weighed, after 16 days, less by 29 per cent than the seed before germination. The same phenomenon is observed in the process of malting, which is in fact the artificial germination of barley, the malt produced always weighing considerably less than the grain from which it was obtained. It was believed by Saussure, and the older investigators, that the carbonic acid evolved was entirely produced from starch and sugar; and as these substances may be viewed as compounds of carbon and water, the change was very simply explained by supposing that the carbon was oxidised and converted into carbonic acid and its water eliminated. But this hypothesis is incapable of explaining all the phenomena observed; for woody fibre, which is one of the chief constituents of the young plant, contains more carbon than the starch and sugar from which it must have been produced, and we are, therefore, forced to admit that the action must be more complicated. There is every reason to believe that the nitrogenous constituents of the seed are most abundantly oxidized, for they are remarkably prone to change; but the action of the air is not confined to them, and it appears most probable that all the substances take part in the decomposition, and the process of germination may, in some respects, be compared to decay or putrefaction, which, like it, is attended by the absorption of oxygen and evolution of carbonic acid; but while in the latter case the residual substances remain in a useless state, in the former they at once become part of a new organism.

Changes occurring during the After-growth of the Plant.—When the plant has developed its roots and leaves, and exhausted the store of materials laid up for it in the seed, it begins to derive its subsistence from the surrounding air, and to absorb carbonic acid, water, ammonia, and nitric acid, and to decompose and convert them into the different constituents of its tissues. These changes take place slowly at first, and more rapidly as the organs fitted for the elaboration of its food are developed. The roots and the leaves are equally active in performing this duty, the former absorbing the mineral matters along with the carbonic acid, ammonia, nitric acid, and moisture in the soil, or the manure added to it; the latter gathering the gaseous substances existing in the air. Each of these undergoes a series of changes claiming our consideration.

Decomposition of Carbonic Acid.—Carbonic acid, which appears to be absorbed with equal readiness by the roots, leaves, and stems, undergoes immediate decomposition, its carbon being retained, and its oxygen, in whole or in part, evolved into the air. This decomposition occurs only under the action of the sun's rays, and has been found to be proportionate to the amount of light to which the plant is exposed. It takes place only in the green parts of plants, for though the roots absorb carbonic acid, they cannot decompose it, or evolve oxygen; and the coloured parts, the flowers, fruits, etc., have an entirely opposite effect, absorbing oxygen and giving off carbonic acid. The absorption of carbonic acid and escape of oxygen has been proved by numerous direct experiments by Saussure and others, in which both atmospheric air and artificial mixtures containing an increased quantity of carbonic acid have been employed. Saussure allowed seven plants of periwinkle (Vinca minor ) to vegetate in an atmosphere containing 7·5 per cent of carbonic acid for six days, during each of which the apparatus was exposed for six hours to the sun's rays. The air was analysed both before and after the experiment, and the results obtained were—

Volume of the air.Nitrogen.Oxygen.Carbonic Acid.
Before the experiment,5746 4199 1116 431
After        "5746 4338 1408 0
————————
Difference,0 +139 +292 -431

In this experiment the whole of the carbonic acid, amounting to 431 volumes, was absorbed, but only 292 volumes of oxygen were given off. Had the carbonic acid been entirely decomposed, and all its oxygen eliminated, its volume would have been equal to that of the acid, or 431, so that in this instance 139 volumes of the oxygen of the carbonic acid have been retained to form part of the tissues of the plant. On the other hand, the nitrogen is found to be increased after the experiment. It might be supposed that the nitrogen evolved had been derived from the decomposition of the nitrogenous constituents of the plant, but this cannot be the true explanation, because in this particular case it greatly exceeded the whole nitrogen contained in the plants experimented on. Its source is not well understood, but Boussingault supposes it to have existed in the interstices of the plant, and to have escaped during the course of the experiment. Saussure found that the oak, the horse-chesnut, and other plants, absorb oxygen and give off carbonic acid in less volumes than the oxygen, while the house-leek and the cactus absorb oxygen without evolving carbonic acid. The absorption and decomposition of carbonic acid takes place only during the day, and matters are entirely reversed during the night, when oxygen is absorbed and carbonic acid eliminated from all parts of the plants.

Although the action occurring during the night is the reverse of that which takes place during the day, it is in no degree to be attributed to a re-oxidation of the carbon which had been deposited in the tissues of the plant. It appears, on the contrary, to be a purely mechanical, and not a chemical process. During the night the sap continues to circulate through the vessels of the plant, and moisture, carrying with it carbonic acid in solution, is absorbed by the roots; but when it reaches the leaves, where the sun's light would have caused its decomposition during the day, it is again exhaled unchanged. The oxygen absorbed during the night must, however, take part in some chemical processes, for if it were merely mechanical, the absorption would not be confined to that gas alone, but would be participated in by the other constituents of the air. Moreover, the amount of absorption varies greatly in different plants—being scarcely appreciable in some, and very abundant in others. Plants containing volatile oils, which are readily converted into resins by the action of oxygen, or those containing tannin or other readily oxidizable substances, take up the largest quantity. This is remarkably illustrated by an experiment in which the leaves of the Agave americana, after twenty-four hours' exposure in the dark, were found to have absorbed only 0·3 of their volume of oxygen, while those of the fir, in which volatile oil is abundant, had taken up twice, and those of the oak, containing tannin, eighteen times as much oxygen.

In the flowers, both by day and night, there is a constant absorption of oxygen, and evolution of carbonic acid. In fact, an active oxidation is going on, attended by the evolution of heat, which, in the Arum maculatum  and some other plants, is so great as to raise the temperature of the flower 10° or 12° above that of the surrounding air.

Decomposition of Water in the Plant.—In addition to the function which water performs in the plant, as the solvent of the different substances which form its nutriment, and hence as the medium through which they pass into its organs, it serves also as a direct food, undergoing decomposition, and yielding hydrogen to the organic substances. Its constituents, along with those of the carbonic acid absorbed, undergo a variety of transformations, and form the principal part of the non-nitrogenous constituents. It has been already observed that starch, sugar, and the other allied substances, may be considered as compounds of carbon with water; and they might be supposed to owe their origin to the carbonic acid losing the whole of its oxygen, and direct combination then ensuing between the residual carbon and a certain proportion of water; but this would imply that the latter substance undergoes no decomposition, and though undoubtedly the simplest view of the case, it is by no means the most probable. It is much more likely that the carbonic acid is only partially decomposed, half its oxygen being separated, and replaced by hydrogen, produced by the decomposition of a certain quantity of water into its elements. Thus, for instance, sugar may be produced from twelve equivalents of carbonic acid and twelve equivalents of water, twenty-four equivalents of oxygen being eliminated, as thus represented:

12 equivalents of carbonic acid,C 12 O 12 O 12
12 "water,H 12 O 12
1 "sugar, and 24 of ox.C 12 H 12 O 12  + O 24

It must not be supposed that we are in a condition to assert that sugar is really produced in the manner here shown, the illustration being given merely for the purpose of pointing out how it may be supposed to occur, and on a similar principle it is possible to explain the formation of most other vegetable compounds; and this subject has been very fully discussed by the late Dr. Gregory, in his "Handbook of Organic Chemistry." That water must be decomposed, is evident from the fact, established by analysis, that the hydrogen of the plant generally exceeds the quantity required to form water with its oxygen, so that this excess at least must be produced by the decomposition of water. The hydrogen of the volatile oils, many of which contain no oxygen, and that of the fats, which contain only a small quantity, must manifestly be obtained in a similar manner.

Decomposition of Ammonia.—The nitrogenous or albuminous compounds of vegetables must necessarily obtain their nitrogen from the decomposition either of ammonia or nitric acid, experiment having distinctly shown that they are incapable of absorbing it in the free state from the atmosphere. It has been clearly ascertained that the albuminous substances do not contain ammonia, and it is hence apparent that a complete decomposition of that substance must take place in the plant. No doubt carbonic acid and water take part with it in these changes, which must be of a very complex character, and in the present state of our knowledge it seems hopeless to attempt any explanation of them.

Decomposition of Nitric Acid.—Chemists are not entirely at one as to whether nitric acid is directly absorbed by the plant, or is first converted into ammonia. But there are certain facts connected with the chemistry of the soil, to be afterwards referred to, which seem to us to leave no doubt that it may be directly absorbed; and in that case it must be decomposed, its oxygen being eliminated, and the nitrogen taking part with carbon and hydrogen in the formation of the organic compounds. It must be clearly understood that while such changes as those described manifestly must take place, the explanations of them which have been attempted by various chemists are not to be accepted as determinately established facts ; they are at present no more than hypothetical views which have been expressed chiefly with the intention of presenting some definite idea to the mind, and are unsupported by absolute proof; they are only inferences drawn from the general bearings of known facts, and not facts themselves. Although, therefore, they are to be received with caution, they have advantages in so far as they present the matter to us in a somewhat more tangible form than the vague general statements which are all that could otherwise be made.

Vegetable Life in the Forests of the Great Islands

HAVE  said that under the same parallels of latitude, or under neighbouring parallels, the physiognomy of the virgin forests was everywhere nearly the same, and hence we must study from a point close at hand the species which compose them, to determine the distinctive characters of the great agglomerations of vegetables peculiar to different  countries. And yet the traveller who, after having explored the primeval forests of Africa and Asia, should be transported to the wild and wooded regions of the great Indian Archipelago and the Pacific Ocean, could not fail to be struck with the novel spectacle presented to his gaze. Undoubtedly he would meet, at first, with a great number of plants not unknown to him; but he would not fail to discover many others which he had not hitherto observed, and especially would he contemplate with astonishment—perhaps with admiration—the chaos of this rich, various, dense, but disordered vegetation. It seems, in truth, as if within these “summer isles of Eden” Nature had hastened to accumulate her choicest products, and feeling herself restricted within narrow limits, had carefully laboured not to lose the smallest particle of space—not even of the aërial territory, if I may so speak—allotted to her. Not only are the trees set in the closest possible array, but they struggle with wonderful effort to develop the exuberance of their strength. Nearly all display an abundant and persistent foliage; their branches are, in general, thick and spongy, and begin to shoot at the base of the trunk; in such wise that the lower boughs extend close to the ground, and by interlacing with those of neighbouring trees, form impenetrable thickets. Many send forth, from their trunk and their branches, frail flexible roots like the lianas, which descend to the earth, plant themselves in the soil, and contribute to render the forests absolutely impervious. Nor is this all; the plants grow there, literally, one upon another. Nowhere, under the Tropics, does one see a similar profusion of epiphytous plants; not a single tree but is invaded by the close-clinging roots and flexible ramifications of these parasites, mingled with brightly-blossoming lianas, whose multifold stems are of immeasurable length. Species worthy of note, either on account of their beauty, their various uses, or formidable poisonous properties, and belonging to widely-differing families, abound, moreover, in these perennial forests.

Ceylon, which has justly been named by the Orientals “a pearl detached from Hindostan,” so admirable is its situation, so marvellous is its fertility, so exhaustless its mineral wealth, is the native country  of the Laurus cinnamomum —which was early transplanted to the neighbouring continent—and of the Artocarpus, or Bread-fruit tree, one of the most curious and most useful plants of this region.

enlarge-image
Bread-fruit Tree of Ceylon (Artocarpus incisa). 
Bread-fruit Tree of Ceylon  (Artocarpus incisa ).

The Bread-fruit Tree (Artocarpus incisa ) is a tree of the family Muriaceæ, some 45 to 55 feet high. Make an incision in its bark, wherever you will, and it exudes a white lacteal fluid, which hardens on exposure to the air. Its branches are very numerous, and those nearest its base attain a considerable length. Its leaves are large, consistent, and somewhat deeply cut. It owes its name of “Bread-fruit tree” to its ovoid or rounded fruit, about the size of an ostrich's egg, which forms the staple food of the Cingalese. When fully ripe, the pulp or flesh is white, firm, farinaceous, and very agreeable to the  taste. The natives boil it whole, or cut it into slices for roasting, and prepare it for the table in numerous other modes. Two or three trees, it is said, suffice for the provisioning of one man. My readers will remember that its introduction in the West Indian Islands was signalized by the famous Mutiny of the Bounty, and led indirectly to the settlement of Pitcairn's Island; thus originating a strange and sufficiently poetical romance.

In the forests of Ceylon also flourish the Cambogia Guttu, the Stalagmites Cambogioides, and the Garcinia morella  (family Guttiferæ), whence camboge is extracted. This substance, at once medicinal and tinctorial, exudes in a liquid state from wounds made in the bark of the trees; it solidifies spontaneously in the vessels wherein it is collected.

Immense forests overspread the humid plains of Sumatra. They are constituted in the main of numerous species of Fig-trees (Ficoidæ), whose abundant and persistent leaves form an obscure vault, impenetrable by the sun's “golden arrows.” Above this leafy dome shoot the rigid trunks of trees of lofty stature. Of these, the most remarkable, perhaps, is the Ipo-antiar (Antiaris toxicaria ), whose juice, after having undergone certain preparations, becomes one of the deadliest known poisons. It was for a long time unknown with what substance the Malays envenomed their arrows and their famous kris, or crease; nor was it until the beginning of the present century that the traveller Leschenault ascertained, not without difficulty, that it had for its basis the juice of a very tall tree, with decaying leaves, to which he gave the name of Antiaris toxicaria. This is the celebrated Upas, whose deadly properties were formerly exaggerated in so many wonderful fables. The poison is prepared in an earthen vessel, and mixed up with certain quantities of the seed of the pimento and the pepper tree, and the roots of various kinds of ginger. These are mixed together slowly, except the pimento-grains, which are precipitated one by one to the bottom of the vessel by means of a small stick. Each grain produces a slight fermentation, and rises to the surface. It is then extracted, to be plunged anew into the mixture, and this process is eight or nine times repeated; after which the mixture is complete. It appears that the Upas-antiar, taken internally, acts at first as a purgative, but afterwards its influence extends to the brain, and produces death with frightful tetanic convulsions. Introduced into the blood through a wound, it kills small animals in a few moments, and men in a few hours.

enlarge-image
1. Nipa fruticans. 2. Sugar Palm (Areca saccharifera).
3. Ipo-Antiar (Antiaris toxicaria). 
1. Nipa fruticans.  2. Sugar Palm (Areca saccharifera ).  3. Ipo-Antiar (Antiaris toxicaria ).

Marvel-loving writers formerly asserted that this deadly poison was employed in the execution of criminals, who, however, received a pardon if they contrived to reach a tree, and bring back a supply of its venom. Birds, it was said, dropped dead while flying over it—as was formerly told of the pestilential waters of the Dead Sea—and  the whole country around was desolated by its noxious effluvia. But the fact is, the upas tree is merely a tree with poisonous secretions, and in no way affects the atmosphere of the locality where it lives.

A not less terrible poison is furnished by the Liana Tieuté (Strychnos tieuté), a member of the family Loganiaceæ. It has an exceedingly long stem, but does not yield, like the upas, a whitish milky juice. Its voluminous roots are covered with a thin reddish bark, of a peculiarly bitter taste. By boiling these roots the Javanese obtain the poisonous resin called in Malaysia Upas tieuté, and which was at one time supposed to be identical with the essential element introduced by the Indians of South America into their famous Ourari  or Wourali. Sir Richard Schomburgk, however, has shown that the latter is obtained from the Strychnos toxifera, a native of Guiana.

There are several other species of Strychnos; all with flattened, disc-like, and silky seeds, surrounded by pulp. S. nux vomica, a moderate-sized tree, with fruit much like an orange in appearance, furnishes the valuable medicine and fatal poison—for it is both—called Nux vomica. The seeds have an intensely bitter taste, owing to the presence of two most virulent poisons, Strychnia  and Brucia ; but the pulp is innocuous, and greedily devoured by birds. Strychnos Colubrina, a native of Malabar, furnished a variety of Snakewood, which in cases of bites by serpents is esteemed an infallible remedy. S. Pseudo-quina, which flourishes in Brazil, yields a bark scarcely inferior in value as a tonic and a febrifuge to quinine.

 

I have spoken of the abundance and variety of the epiphytous plants which grow profusely in the islands of the Indian Ocean. In Sumatra and in Borneo, the more venerable trees are clothed in a rich garment of lycopodiums and ferns, and these often glow with dazzling orchidaceous flowers, while by their side flourish strange aroidaceæ, with climbing crawling stems, and aërial suckers. But of all these brilliant parasites, the most extraordinary, without doubt, is the Rafflesia Arnoldi —a plant without any stem, which grows along the surface of the ground upon the roots of the lianas, and principally  of the lissus, a species of vine peculiar to tropical countries. It was discovered by Dr. Arnold, while in attendance upon Sir Stamford Raffles, Governor of Java. It produces only a fleshy flower, of a wine-like colour, with an intolerably disgusting odour; but it acquires extraordinary, and one might say monstrous dimensions, for it seldom measures less than a yard in diameter, and its weight frequently exceeds four pounds.

Upon the humid coasts of Borneo and Sumatra, the Casuarinas  mingle their weeping branches with those of the mangroves and fig-trees. Palms are common in these two great islands, as well as at Ceylon and at Java. I may mention among the most useful the Nipa fruticans  and the Sugar Palm (Areca saccharifera ). The transformed leaves which accompany the inflorescence of the Nipa are brimful of a sugared and effervescent liquid, which is extracted by pressure, and converted into a palm wine of indifferent quality, consumed in great quantities in the Sunda Archipelago. A very sweet liquid, a species of syrup fit for the confection of dainty sweetmeats, escapes from incisions made into the floral envelopes of the Areca saccharifera. A tree-wax, analogous to that of the Croton sebiferum, is furnished by the tree which the natives of Borneo designate Pallagrar-Minjok (Dipterocarpus trinervis ). And, finally, it is at Borneo and at Sumatra we meet with the Dryobabanops camphora, whence is procured a species of camphor preferred by the Chinese to that of the Laurus camphora ; the Urceola elastica, whose milky sap indurates into a kind of caoutchouc, called Suitawan; and the Isonandra-Percha  (genus Bassia butyracea, family of the Sapotaceæ), which of recent years has become the staple of an extensive commerce. It is from this tree we obtain the valuable product of gutta-percha, which has received such various and ingenious applications, and is scarcely less useful in the arts than in the sciences.

enlarge-image
FLORA OF THE EAST INDIAN ISLANDS:—

1. Rafflesia Arnoldia.
2. Niphobolus pubescens.
3. Phalænopsis amabilis.
4. Ærides suaveolens.
5. Cycas circinnalis.
6. Nepenthes distillatoria.
7. Scindapsus pertusus. 
FLORA OF THE EAST INDIAN ISLANDS:— 
1. Rafflesia Arnoldia.
2. Niphobolus pubescens. 
3. Phalænopsis amabilis.  
4. Ærides suaveolens.
5. Cycas circinnalis.
6. Nepenthes distillatoria.
7. Scindapsus pertusus.

Java is perhaps the most fertile of the Sunda Islands. Immense forests extend over its plains, and climb up its mountain-slopes to an elevation of upwards of 6500 feet. The damp localities are peopled with Clusiaceæ, and with other trees of thick soft trunks and branches. Mangroves and Avicennias thrive upon the littoral. The latter are specially noticeable on account of their roots, which climb to a great distance above the muddy soil, and throw off a number of suckers, not unlike gigantic water-pipes (asperges ). Among the palms most abundant at Java, I confine myself to naming the Borrassus, the Corypha, and the Areca. The Vaquois (a species of Pandanus ), which in stature and appearance resemble the palms, are also widely diffused in that rich and fertile island. In the forests of its interior swarm such splendid Ferns as the Niphobolus pubescens, and such graceful Archids as the Aerides  suaveolens, with its far-shooting fronds and flowers, and the Phalænopsis amabilis. There, too, the traveller pauses before the Cycas circinnalis, whose trunk, upright and cylindrical as a Grecian column, is surmounted by a crest of feathery leaves, each six to seven feet in length, stiff, and cut into numerous strips, somewhat like our native bracken; or he refreshes himself with the pure liquid which the winding Nepenthes distillatoria, or Pitcher plant, collects in its horn-shaped leaves, as a constant source of nutriment for its active life; or, finally, he gazes wonderingly at the Scindapsus pertusus, an epiphytous plant, whose cartilaginous leaves are perforated with an infinity of small circular holes, and which twines itself round the tallest forest-trees in an embrace as close as love's!

The forest-flora of the Moluccas differs but little from that of the Sunda Islands. It presents, however, a few plants particularly calculated to excite our interest. Thus, at Amboyna, the Sago-Palms, with other trees of the same family, accumulate in immense woods, spreading over hundreds of acres. Everybody knows that the pith of this palm is a white farinaceous substance, called sago, which not only enters largely into the daily food of the natives, but forms an important item in the European bill of fare, at least for children and invalids. Amboyna, moreover, is the classic land of spices. The air is thick with “Sabæan odours.” Every breeze comes laden with perfumes. The Nutmeg (Myristica aromatica ), the Clove (Caryophyllus aromaticus ), and the Pepper-plants grow there in a wild state.

In the Philippines vegetation is singularly favoured by the humidity of the climate and the elevation of the temperature, so that the Flora of these richly-endowed islands displays a prodigious variety. Not a single family of tropical plants but is here represented by several species. Hill and valley and plain alike are characterized by the exuberant growth of leaf and fruit and flower; the graceful forms might have enchanted an ancient Greek, the wealth of glowing and intense colour would have fired the imagination of Turner, and defied the palette of Titian or Tintoretto. There are landscapes of such beauty and fertility as the fancy of artist or poet never conceived. Ferns and Orchids are, perhaps, even more abundant here than in the forests of Java, Borneo, or Sumatra. The Bamboo attains to unusual proportions; the Areca (Areca catechu ) raises to the sky its tall shapely stem, crested with plume-like leaves; and the Betel-nut tree supplies in profusion the grains which, mixed with the fruits of the gigantic palm, constitute the Pinangue ; a kind of quid, which the Orientals chew delightedly, and to which they attribute very valuable stomachic and digestive properties. Under the dense shade of the great forests we are amazed by untold numbers of various kinds of plants, all adorned by richly coloured leaves, which invest the scene with a singular charm, nay, with something of a fairy character; and amongst these we single out the Dracæna terminalis, with its blood-empurpled foliage, which, recently introduced into Europe, has already become one of the greatest ornaments of our parks and gardens.

I have previously had occasion to remark the singularity of character which in Australia distinguishes almost every member either of the vegetable or the animal kingdom. I have already said that this immense island-continent seems to have been the chosen theatre for a distinct creative display, where every type differs from the representatives of our scientific classifications in other parts of the globe. The reader has been able to form some idea of the fancifulness of the vegetable forms peculiar to the Australian savannahs. Nor are those which constitute the so-called forests less strangely fantastic. On the southern coast, which is the coolest, the forests are of very moderate  extent. In fact, they may be more correctly described as enormous thickets scattered in tolerably sheltered localities. Most of the trees which compose them have trunks of great feebleness compared with their height, which is often prodigious, and they do not begin to ramify until near their summits. Their bark is smooth, and usually of a grayish-white. Of all their species it can only be said that two—the Stadmannia austral  and the Alectryon —bear fruit which men can eat even under the pressure of hunger. Finally—and this without doubt is the most singular feature of a truly exceptional vegetation—while all the trees and herbaceous plants of the Old and New Worlds develop their leaves horizontally, or on a plane tangent to the cylindrical surface of the trunk or stem, in Australia the leaves of the trees are disposed vertically; in such wise that they give scarcely any shade, and yet are themselves exposed in the very slightest degree to the action of the solar rays. It is owing to this latter circumstance they are always weakly coloured; and thus they give to the densest forests and the most robust trees a sickly tint, a sort of pallor of disease, which saddens the gaze accustomed to the varied tones and vivid hues of the verdure of tropical forests, or to the bold contrasts of light and shade exhibited by the woods of Europe and North America.

The Australian species are comprised in a small number of families, notably in those of the Coniferæ and Myrtaceæ. Certain forests are wholly composed of Casuarinas; others, of Acacias; others again, of Eucalypti. Some of the latter trees may be ranged among the greatest with which botanists are acquainted. The Blue Gum (Eucalyptus globulus ) attains, for instance, the extraordinary stature of upwards of 300 feet, and does not send out a single branch until half this distance from the ground. Its upright cylindrical trunk furnishes a timber much appreciated by ship-wrights, and especially makes admirable masts. The Eucalypti secrete in abundance a white, sugary, and aromatic substance; whence they derive their popular name of “gum trees”—a name which is also bestowed very frequently upon the gum-bearing Acacias.

The family of Coniferæ exhibit themselves in Australia, like every  other group of plants, under strange and novel forms. The shape of those trees is generally fusiform and pyramidal; their leaves are sometimes extraordinarily small, sometimes large and flattened. Many are of great size; none, however, attaining the gigantic proportions of the celebrated columnar Pine of New Caledonia, which Cook's companions mistook for a colossal mass of basaltic pillars, and which Moore, like a true son of industrious Albion, compared to an enormous factory-chimney. This tree exceeds 160 feet in height, and its ramifications, all of the same height, radiate regularly around its trunk, from the base even to the summit.

enlarge-image
1. Ravenala Madagascariensis. 2. Heritiera argentea. 3.
Tanghin. 
1. Ravenala Madagascariensis.  2. Heritiera argentea.  3. Tanghin.

 

enlarge-image
A FOREST IN MADAGASCAR. 
A FOREST IN MADAGASCAR.

I have now to ask the reader's companionship on an excursion  into the forests of the great African island of Madagascar. The insalubrity of the climate and the jealous inhospitality of the inhabitants will not permit us to penetrate far into their luxuriant depths; but the most superficial glance will satisfy us upon their wild magnificence and the original variety of their superb flora.[167]

We should seek in vain among their leafy, blossoming glades, for the famous Manchineal, a member of the American Euphorbiaceæ, which holds a high place in the records of vegetable poisons; but the toxicological amateur will find ample compensation in examining the formidable Tanghin,[168] whose deadly juice, mixed with some other substances, plays an important part in the judicial ordeals popular among the Malagasy.

The Tanghin, or Tanguen (T. venenifera ), is the only plant of its genus, and is confined to Madagascar. It is described as a tree with smooth alternate leaves of moderate thickness, clustered towards the points of the branches, with large terminal cymes of flowers, having a salver-shaped corolla, with rose-coloured lobes. The ovary is twofold, with a long style and thick stigma; but usually only one attains to perfection, and forms an ellipsoid fruit, somewhat pointed at the ends, invested in a smooth purplish-green skin, and containing a hard stone surrounded by a thick fibrous pulp. The poisonous seed of the Tanghin is esteemed by the natives an infallible criterion of guilt or innocence. After being pounded, a small piece is swallowed by the supposed criminal. If he be cursed with a strong stomach, which retains the poison, he speedily dies, and is held guilty; if his feeble digestion rejects it, he necessarily escapes, and his innocence is considered proven.

Beneficent Nature has planted by the side of this fatal tree a species of infinite value, the Ravenala Madagascariensis, or “Traveller's-Tree,” which derives the latter designation from the base of the petiole of its large leaves, expanded and hollowed out into a kind of gutter, being constantly filled with fresh water, and serving as a reservoir for the thirsty wayfarer. The Vacquois, or Vacoa (Pandanus  utilis ), one of the Screw-Pines, is of much utility to the natives, who fabricate sacks and bags out of its tenacious leaves. The manufacture of these bags is a source of comparative wealth for the poorer inhabitants of Madagascar, and to a still greater extent for those of Réunion and the Mauritius, whence they are exported annually by millions.

The Malagasy forests also include several resinous species; among others, the Copal-Tree, which furnishes the well-known gum used in Europe as a varnish; and the Vahea, a genus of Apocynaceæ, yielding caoutchouc, which will hereafter figure largely in the exports from this magnificent island. There are two species, namely, Vahea Madagascariensis —the “Voua Héri” of the natives—and Vahea gummifera. Numerous lianas, and a multitude of epiphytous plants, ferns, and orchids, envelop and intertangle the trunks of the great trees. I shall specify only the Beaded Liana (Abrus precatorius ), whose small hard fruits, rounded and of a scarlet red, make graceful wreaths and necklaces; the Angræcum sesquipedale  (an orchid), with bright irregular flowers; and the Angræcum fragrans, whose perfumed leaves supply a wholesome and savoury infusion. Finally, the Heritiera argentea, a tree about as large as our lindens, which certain botanists place among the Byttneriaceæ, and others among the Sterculiaceæ, is noticeable on account of its abundant foliage glittering silver-white.


[167] Rev. W. Ellis, “Three Visits to Madagascar.”

[168] Order, Apocynaceæ.

The Proximate Constituents of Plants

The substances absorbed by the plant, which are of simple composition, and contain only two elements, are elaborated within it, and converted into the many complicated compounds of which its mass is composed. Some of these, as, for example, the colouring matters of madder and indigo, the narcotic principle of the poppy, &c., are confined to a single species, or small group of plants, while others are found in all plants, and form the main bulk of their tissues. The latter are the only substances which claim notice in a treatise like the present. They have been divided into three great classes, of widely different properties, composition, and functions.

1st. The Saccharine and Amylaceous Constituents.—These substances are compounds of carbon, hydrogen, and oxygen, and all possess a certain degree of similarity in composition, the quantities of hydrogen and oxygen they contain being always in the proportion required to form water, so that they may be considered as compounds of carbon and water; not that it can be asserted that they actually do contain water, as such, for of that there is no evidence, but only that its elements are present in the proportion to form it.

Cellulose.—This substance forms the fundamental part of all plants. It is the principal constituent of woody fibre, and is found in a state of purity in the fibre of cotton and flax, and in the pith of plants; but in wood it is generally contaminated with another substance, which has received the name incrusting matter, because it is deposited in and around the cells of which the plant is in part composed. Cellulose is insoluble in all menstrua, but, when boiled for a long time with sulphuric acid, is converted into a substance called dextrine. Cellulose consists of—

From pith of Elder-tree.Spongioles of roots.
Carbon 43·37 43·00
Hydrogen 6·04 6·18
Oxygen 50·59 50·82
——————
100·00 100·00

It is represented chemically by the formula, C 24 H 21 O 21 , which shows it to be a compound of 24 atoms of carbon with 21 of hydrogen and 21 of oxygen.

Incrusting matter.—Large quantities of this substance enter into the composition of all plants. Of its chemical nature little is known, as it cannot be obtained separate from cellulose, but it is analogous to that substance in its composition, and probably contains hydrogen and oxygen in the proportion to form water.

Starch.—Starch is one of the most abundant constituents of plants, and is found in most seeds, as those of the cereals and the leguminous plants; in the tubers of the potatoe, the bulbs of tulips, &c. &c. It is obtained by placing a quantity of wheat flour in a bag, and kneading it under a gentle stream of water. When the water is allowed to stand, it deposits the starch as a fine white powder, which, when examined by the microscope, is found to be composed of minute grains, formed of concentric layers deposited on one another. These grains vary considerably in size and structure in different plants; but in the same plant they are generally so much alike as to admit of their recognition by a practised observer. They were formerly believed to be composed of an external coating of a substance insoluble in water, and containing in their interior a soluble kernel; but this opinion has been refuted, and distinct evidence been brought to show that the exterior and interior of the globules are identical in chemical properties. Starch is insoluble in cold water, but by boiling, it dissolves, forming a thick paste. By long continued boiling with water containing a small quantity of acid, it is completely dissolved and converted into dextrine, and eventually into sugar. The same change is produced by the action of fermenting substances, such as the extract of malt; when heated in the dry state to a temperature of about 390 Fahr., it becomes soluble in cold water. It is distinguished by giving a brilliant blue compound with iodine. Starch contains—

Carbon 44·47
Hydrogen 6·28
Oxygen 49·25
———
100·00

and its composition is represented by the formula C 12 H 10 O 10 , so that it differs but little from cellulose in composition, although its chemical functions in the plant are extremely different. It is connected with some of the most important changes which occur in the growing plants, and by a series of remarkable transformations is converted into sugar and other important compounds.

Lichen Starch  is found in most species of lichens, and is distinguished from common starch by producing a green colour with iodine. Its composition is the same as that of ordinary starch.

Inuline.—The species of starch to which this name is given is characterised by its dissolving in boiling water, and giving a white pulverulent deposit in cooling. It is found in the tuber of the dahlia, in the dandelion, and some other plants. Its composition is identical with that of cellulose, and its formula is C 24 H 21 O 21 .

Gum  is excreted from various plants as a thick fluid, which dries up into transparent masses. Its composition is identical with that of starch. It dissolves readily in cold water, and is converted into sugar by long continued boiling with acids. Its properties are best marked in gum arabic, which is obtained from various species of acacia; that from other plants differs to some extent, although its chemical composition is the same.

Dextrine.—When starch is exposed to a heat of about 400°, or when treated with sulphuric acid, or with a substance extracted from malt called diastase, it is converted into dextrine. It may also be obtained from cellulose by a similar treatment. The dextrine so obtained has the same composition as the starch from which it is produced, but its properties more nearly resemble those of gum. It plays a very important part in the process of germination, and may be converted into sugar on the one hand, and apparently also into starch on the other.

Sugar.—Under this name are included four or five distinct substances, of which the most important are, cane sugar, grape sugar, and the uncrystallisable sugar found in many plants.

Cane Sugar.—This variety of sugar, as its name implies, is found most abundantly in the sugar cane, but it occurs also in the maple, beet-root, and various species of palms, from all of which it is extracted on the large scale. It is extremely soluble in water, and can be obtained in large transparent prismatic crystals, as in common sugar-candy. It swells up, and is converted into a brown substance called caramel, when heated, and by contact with fermenting substances, yields alcohol and carbonic acid. It contains—

Carbon 42·22
Hydrogen 6·60
Oxygen 51·18
———
100·00

and its chemical formula is C 12 H 11 O 11 .

Grape Sugar  is met with in the grape, and most other fruits, as well as in honey. It is produced artificially when starch is boiled for a long time with sulphuric acid, or treated with a large quantity of diastase. It is less soluble in water than cane sugar, and crystallises in small round grains. Its composition, when dried at 284°, is—

Carbon 40·00
Hydrogen 6·66
Oxygen 53·34
———
100·00

and its formula is C 12 H 12 O 12 ; but when crystallised it contains two equivalents of water, and is then represented by the formula C 12 H 12 O 12  + 2H 2 O.

The uncrystallisable sugar of plants is closely allied to grape sugar, and, so far as at present known, has the same composition, although, from the difficulty of obtaining it quite free from crystallised sugar, this is still uncertain.

Mucilage  is the name applied to the substance existing in linseed, and in many other seeds, and which communicates to them the property of swelling up and becoming gelatinous when treated with water. It is found in a state of considerable purity in gum tragacanth and some other gums. Its composition is not known with absolute certainty, but it is either C 24 H 19 O 19 , or C 12 H 10 O 10 ; and in the latter case it must be identical with starch and gum.

It will be observed that all the substances belonging to this class are very closely related in chemical composition, some of them, as starch and gum, though easily distinguished by their properties, being identical in constitution, while others only differ in the quantity of water, or of its elements which they contain. In fact, they may all be considered as compounds of carbon and water, and their relations are, perhaps, more distinctly seen when their formulæ are written so as to show this, as is done in the following table, in the second column of which those containing twelve equivalents of carbon are doubled, so as to make them comparable with cellulose:—

Water.
Grape sugar,C 12 H 12 O 12 C 24 H 24 O 24 C 24  + 24
Cane sugar,C 12 H 11 O 11 C 24 H 22 O 22 C 24  + 22
Cellulose,C 24 H 21 O 21 C 24 H 21 O 21 C 24  + 21
Inuline,C 24 H 21 O 21 C 24 H 21 O 21 C 24  + 21
Starch,C 12 H 10 O 10 C 24 H 20 O 20 C 24  + 20
Dextrine,C 12 H 10 O 10 C 24 H 20 O 20 C 24  + 20
Gum,C 12 H 10 O 10 C 24 H 20 O 20 C 24  + 20
Mucilage,C 12 H 10 O 10 C 24 H 20 O 20 C 24  + 20

The relation between these substances being so close, it is not difficult to understand how one may be converted into another by the addition or subtraction of water. Thus, cellulose has only to absorb an equivalent of water to become grape sugar, or to lose an equivalent in order to be converted into starch, and we shall afterwards see that such changes do actually occur in the plant during the process of germination.

Pectine and Pectic Acid.—These substances are met with in many fruits and roots, as, for instance, in the apple, the carrot, and the turnip. They differ from the starch group in containing more oxygen than is required to form water along with their hydrogen; but their exact composition is still uncertain, and they undergo numerous changes during the ripening of the fruit.

2d. Oily or Fatty Matters.—The oily constituents of plants form a rather extensive group of substances all closely allied, but distinguished by minor differences in properties and constitution. Some of them are very widely distributed throughout the vegetable kingdom, but others are almost peculiar to individual plants. They are all compounds of carbon, hydrogen, and oxygen, and are at once distinguished from the preceding class, by containing much less oxygen than is required to form water with their hydrogen. The principal constituents of the fatty matters and oils of plants are three substances, called stearine, margarine, and oleine, the two former solids, the latter a fluid; and they rarely, if ever, occur alone, but are mixed together in variable proportions, and the fluidity of the oils is due principally to the quantity of the last which they contain. If olive oil be exposed to cold, it is seen to become partially solid; and if it be then pressed, a fluid flows out, and a crystalline substance remains; the former is oleine, though not absolutely pure, and the latter margarine. The perfect separation of these substances involves a variety of troublesome chemical processes; and when it has been effected, it is found that each of them is a compound of a peculiar acid, with another substance having a sweet taste, and which has received the name of glycerine, or the sweet principle of oil. Glycerine, as it exists in the fats, appears to be a compound of C 3 H 2 O, and its properties are the same from whatever source it is obtained. The acids separated from it are known by the names of margaric, stearic, and oleic acids.

Margaric Acid  is best obtained pure by boiling olive oil with an alkali until it is saponified, and decomposing the soap with an acid, expressing the margaric acid, which separates, and crystallising it from alcohol. It is a white crystalline fusible solid, insoluble in water, but soluble in alcohol and in solutions of the alkalies. Its composition is—

Carbon 75·56
Hydrogen 12·59
Oxygen 11·85
———
100·00

and its formula C 34 H 34 O 4 .

Stearic Acid.—Although this acid exists in many plants, it is most conveniently extracted from lard. It is a crystalline solid less fusible than margaric acid, but closely resembling it in its other properties. Its formula is C 36 H 36 O 4 .

Oleic Acid.—Under this name two different substances appear to be included. It has been applied generally to the fluid acids of all oils, while it would appear that the drying and non-drying oils actually contain substances of different composition. The acid extracted from olive oil appears to have the formula C 36 H 34 O 4 , while that from linseed oil is C 46 H 38 O 6 , but this is still doubtful.

Other fatty acids have been detected in palm oil, cocoa-nut oil, &c. &c., which so closely resemble margaric and stearic acids as to be easily confounded with them. Though presenting many points of interest, it is unnecessary to describe them in detail here.

Wax  is a substance closely allied to the oils. It consists of two substances, cerine and myricine, which are separated from one another by boiling alcohol, in which the former is more soluble. They are extremely complex in composition, the former consisting principally of an acid similar to the fatty acids, called cerotic acid, and containing C 54 H 54 O 4 . The latter has the formula C 92 H 92 O 4 . The wax found in the leaves of the lilac and other plants appears to consist of myricine, while that extracted from the sugar-cane is said to be different, and to have the formula C 48 H 50 O 2 . It is probable that other plants contain different sorts of wax, but their investigation is still so incomplete, that nothing definite can be said regarding them. Wax and fats appear to be produced in the plant from starch and sugar; at least it is unquestionable that the bee is capable of producing the former from sugar, and we shall afterwards see that a similar change is most probably produced in the plant. The fatty matters contained in animals are identical with those of plants.

3d. Nitrogenous or Albuminous Constituents of Plants and Animals.—The nitrogenous constituents of plants and animals are so closely allied, both in properties and composition, that they may be most advantageously considered together.

Albumen.—Vegetable albumen is found dissolved in the juices of most plants, and is abundant in that of the potato, the turnip, and wheat. In these juices it exists in a soluble state, but when its solution is heated to about 150°, it coagulates into a flocky insoluble substance. It is also thrown down by acids and alcohol. Coagulated albumen is soluble in alkalies and in nitric acid. Animal albumen exists in the white of eggs, the serum of blood, and the juice of flesh; and from all these sources is scarcely distinguishable in its properties from vegetable albumen.

It is a substance of very complicated composition, and chemists are not agreed as to the formula by which its constitution is to be expressed, a difficulty which occurs also with most of the other nitrogenous compounds. The results of the analyses of albumen from different sources are however quite identical, as may be seen from those subjoined—

From Wheat.From Potatoes.From Blood.From White of Egg.
Carbon 53·7 53·1 53·4 53·0
Hydrogen 7·1 7·2 7·0 7·1
Nitrogen 15·6 ...15·5 15·6
Oxygen }         {...22·1 22·9
Sulphur }23·6{0·97 1·6 1·1
Phosphorus }         {...0·4 0·3
——————
100·0 100·0 100·0

Closely allied to vegetable albumen is the substance known by the name of glutin, which is obtained by boiling the gluten of wheat with alcohol. It appears to be a sort of coagulated albumen, with which its composition completely agrees.

Vegetable Fibrine.—If a quantity of wheat flour be tied up in a piece of cloth, and kneaded for some time under water, the starch it contains is gradually washed out, and there remains a quantity of a glutinous substance called gluten. When this is boiled with alcohol, the glutin  above referred to is extracted, and vegetable fibrine is left. It dissolves in dilute potash, and on the addition of acetic acid is deposited in a pure state. Treated with hydrochloric acid, diluted with ten times its weight of water, it swells up into a jelly-like mass. When boiled or preserved for a long time under water, it cannot be distinguished from coagulated albumen.

Animal Fibrine  exists in the blood and the muscles, and agrees in all its characters and composition with vegetable fibrine, as is shown by the subjoined analyses—

Wheat Flour.Blood.Flesh.
Carbon 53·1 52·5 53·3
Hydrogen 7·0 6·9 7·1
Nitrogen 15·6 15·5 15·3
Oxygen 23·2 24·0 23·1
Sulphur 1·1 1·1 1·2
——————
100·0 100·0 100·0

Caseine.—Vegetable caseine exists abundantly in most plants, especially in the seeds, and remains in the juice after albumen has been precipitated by heat, from which it may be separated in flocks by the addition of an acid. It has been obtained for chemical examination, principally from peas and beans, and from the almond and oats. When prepared from the pea it has been called legumine, from almonds emulsine, and from oats avenine ; but they are all three identical in their properties, although formerly believed to be different, and distinguished by these names. Vegetable caseine is best obtained by treating peas or beans with hot water, and straining the fluid. On standing, the starch held in suspension is deposited, and the caseine is retained in solution in the alkaline fluid; by the addition of an acid it is precipitated as a thick curd. Caseine is insoluble in water, but dissolves readily in alkalies; its solution is not coagulated by heat, but, on evaporation, becomes covered with a thin pellicle, which is renewed as often as it is removed.

Animal Caseine  is the principal constituent of milk, and is obtained by the cautious addition of an acid to skimmed milk, by which it is precipitated as a thick white curd. It is also obtained by the use of rennet, and the process of curding milk is simply the coagulation of its caseine. It is soluble in alkalies, and precipitated from its solution by acids, and in all other respects agrees with vegetable caseine.

The composition of animal caseine has been well ascertained, but considerable doubt still exists as to that of vegetable caseine, owing to the difficulty of obtaining it absolutely pure. The analyses of different chemists give rather discordant results, but we have given those which appear most trustworthy—

From Peas.
Carbon 50·6 50·7
Hydrogen 6·8 6·6
Nitrogen 16·5 15·8
Oxygen 25·6 23·8
Sulphur 0·5 0·8
Phosphorus ...2·3
————
100·0 100·0

Other results differ considerably from these, and some observers have even obtained as much as eighteen per cent of nitrogen and fifty-three of carbon.

The composition of animal caseine differs from this principally in the amount of carbon. Its composition is—

Carbon 53·6
Hydrogen 7·1
Nitrogen 15·8
Oxygen 22·5
Sulphur 1·0
——
100·0

The most cursory examination of these analytical numbers is sufficient to show that a very close relation subsists between the different substances just described. Indeed, with the exception of vegetable caseine, they may be said all to present the same composition; and, as already mentioned, there are analyses of it which would class it completely with the others. While, however, the quantities of carbon, hydrogen, nitrogen, and oxygen are the same, differences exist in the sulphur and phosphorus they contain, and which, though very small in quantity, are indubitably essential to them. Much importance has been attributed to these constituents by various chemists, and especially by Mulder, who has endeavoured to make out that all the albuminous substances are compounds of a substance to which he has given the name of proteine, with different quantities of sulphur and phosphorus. The composition of proteine, according to his newest experiments, is—

Carbon 54·0
Hydrogen 7·1
Nitrogen 16·0
Oxygen 21·4
Sulphur 1·5
——
100·0

and is exactly the same from whatever albuminous compound it is obtained. Although the importance of proteine is probably not so great as Mulder supposed, it affords an important illustration of the close similarity of the different substances from which it is obtained, the more especially as there is every reason to believe that the different albuminous compounds are capable of changing into one another, just as starch and sugar are mutually convertible; and the possibility of this change throws much light on many of the phenomena of nutrition in plants and animals. Indeed, it would seem probable that these compounds are formed from their elements by plants only, and are merely assimilated by animals to produce the nitrogenous constituents they contain.

Diastase  is the name applied to a substance existing in malt, and obtained by macerating that substance with cold water, and adding a quantity of alcohol to the fluid, when the diastase is immediately precipitated in white flocks. It is produced during the malting process, and is not found in the unmalted barley. Its chemical composition is unknown, but it is nitrogenous, and is believed to be produced by the decomposition of gluten. If a very small quantity of diastase be mixed with starch suspended in hot water, the starch is found gradually to dissolve, and to pass first into the state of dextrine, then into that of sugar. The change thus effected takes place also in a precisely similar manner in the plant, diastase being produced during the process of germination of all seeds and tubers, for the purpose of effecting this change, and to fulfil other functions less understood, but no doubt equally important. Diastase is found in the seeds only during the period when the starch they contain is passing into sugar; as soon as that change has taken place, its function is ended, and it disappears.

Vegetable Life in the Forests of the Old World

DO  not think that in all Europe, nor, indeed, in the entire Temperate Zone of the Old World, exists such an agglomeration of plants and trees as may merit the appellation of “primeval” or “virgin forest.” At all events, this forest, if it really exists, will assuredly be composed of the very trees which we see every day in our own woods, our fields, our parks, and even in our towns, and which have long ceased  to awaken in us the idea of wild nature. With the woods of Great Britain, France, or Spain we are all familiar:—

“The beam
Of noon is broken there by chestnut boughs
Down the steep verdant sides; the air
So freshened by the leaping stream, which throws
Eternal showers of spray on the mossed roots
Of trees, and veins of turf, and long dark shoots
Of ivy-plants, and fragrant hanging bells
Of hyacinths, and on late anemones
That muffle its wet banks.”[158]

Our poets have sung of the murmurous groves of pines, and the deep dark beech-woods that clothe with shadows the rounded forms of the chalk-hills, and the long alleys of blossoming chestnut, fragrant lime, or sombre yew. Therefore, without losing valuable time in these familiar shades, without pausing before the oak which the history of a thousand years has made immortal, let us rapidly traverse the Corsican forests, where among the twisted leaves of the elms flourishes the gigantic Larician pine; those of Greece, where thrive the pines of Cephalonia and Apollo, and the oaks sacred also to the divinity of Delphi and Dodona—those oaks, dumb to-day, which formerly gave utterance to oracles not less reverend than those of the Pythoness. We will not even suffer ourselves to be delayed among the forests of Eastern Europe, of Asia Minor, and of Persia, where dominate such species as the pine, the beech, and the chestnut. It is not until we have crossed the Indus—that mighty river on whose banks halted the legions of Alexander—that the exuberant vegetation of the Tropical world breaks upon us in all its glorious verdure and prodigious richness, though confined to a comparatively limited area.

The wooded region of the western Ghauts, from Goa to Cape Camorin, exhibits the greatest abundance of plants peculiar to Southern Asia.

enlarge-image
TROPICAL VEGETATION.
1. Calamus Rotang.
2. Bamboos.
3. Borassus flabelliformis.
4. Diospyros ebenum. 
TROPICAL VEGETATION. 
1. Calamus Rotang.    
2. Bamboos.
3. Borassus flabelliformis.
4. Diospyros ebenum.

To form an idea of the variety and potency of the Flora of this region, says M. Lanoye,[159] we must contemplate the specimens immured  in our European gardens, and augment tenfold their etiolated proportions; we must bring together, in the dazzling confusion of Nature, the Mimosas, the Musas, the odorous Screw-pines, the Mangoes, and the Orange trees; twine around their trunks the many-branched stems of the Bignonias, the Nagatelly, the Dictantes-Sambas, and the Lianas which furnish pepper and the betel-nut; group under their shade the most beautiful varieties of Azaleas, Jasmines, and Gardenias; unite those Laurels whence we extract camphor, cassia, and cinnamon, with the red Santul, the Nopals, and the Dragon trees which supply the costly gum-lacs; the Shrubs which give us spikenard, cardamoms, and amome, with those Canes which secrete sugar. Above these masses of flowers, above these sources of honey and perfume, we must next display the immense leaves of the Talipot and the Bourbon-palm, must spread in undulations the aërial palm-crests of the Cocoa-nut and the gigantic Bamboo; must accumulate the sombre verdure of the Teaks and the Tamarinds, and the impenetrable branches of the consecrated Pines. Then, all this being accomplished, we shall still have but a vague and colourless perception of the Indian Flora, and notably of that which clothes the base of the Western Ghauts to the east and to the south of the city of Goa.

The difficulty of picturing to ourselves the entirety of so glorious and rich a scene reveals the impossibility of seizing all its details, of studying one by one all its elements. Our attention, however, will be arrested by a small number of species remarkable above all others by their extraordinary dimensions, the elegance of their bearing, the beauty of their flowers and foliage, or by some peculiar and destructive property.

We notice in the first place several trees whose close relationship cannot be mistaken to the date trees which we have already met with in the open Desert, and which, we may remember, constituted the entire wealth of the inhabitants of the oases. We find representatives of the immense family of palms in every tropical country, and even in the coral islands of the great ocean. India possesses several species. I shall refer only to the Borassus flabelliformis, whose  trunk, 90 to 120 feet in height, is surmounted by a crown of great fan-shaped leaves, folded longitudinally in their first half, cut in the other, and sustained by prickly supports. The other half is made use of by the Hindus in the shape of paper, or rather tablets, on which they write with the point of a stylet. The spadices (clustered flowers), if incised before reaching maturity, yield a liquid which, after fermentation, forms the favourite Indian beverage of “palm wine.”

The Bamboo, the most gigantic of the tropical Gramineæ, is plentifully distributed over India, Indo-China, and China, where it frequently flourishes in considerable masses. In height it equals the loftiest palms. Its culm is smooth, glittering, straight, and flexible, of a beautiful yellow colour, and regularly intersected by annular rings marked by so many brown streaks. It wavers gently to and fro with the impulse of the wind, as if to refresh with its breath the light undulating foliage.

Almost innumerable are the services which this heaven-sent plant renders to the inhabitants of the countries where it flourishes. In hedges or plantations it forms around their abodes a formidable defence. With its stems sawn either in accordance with their diameter, or split longitudinally, the natives not only fabricate a host of utensils and articles of furniture, but build their barks and construct their houses. They extract from the spaces between the joints of the young plant a feculent substance which supplies them with an agreeable nutriment, analogous to sago. A saccharine juice flows spontaneously from the joints formed by the knots; when fermented it becomes alcoholic and heady like hydromel. The bamboo also proves serviceable in the manufacture of mats and cordage. The slender stems are split into thin strips, which are probably softened in water. These strips, woven together, form mats or carpets of extreme solidity.

 

The Banana,[160] like the Bamboo and most of the palms, is a cosmopolitan  plant throughout the tropic world. Its native habitat is supposed to be Asia. The Oriental Christians have a tradition that this tree, which they call the Lignum Vitæ, was that whose fruit was forbidden to our first parents. Hence the name of Musa paradisiaca, given by botanists to one of the two species of the genus; the other is the Banana of the wise men, Musa sapientum. However this may be, it is certain that if the use of the banana was at any time interdicted to man, the prohibition has been annulled for many generations; and its fruits form one of the most wholesome and most general articles of food in tropical countries. Although the wild banana maintains its place honourably in the forests of these regions, it is not a tree, but an herbaceous plant. It propagates itself through its suckers, and its stem perishes immediately after fructification. Its mode of vegetation is analogous to that of the Liliaceæ. From a bulbous and fleshy platform issue, beneath, its fibrous roots; above, enormous leaves, often nearly a yard wide and two to three yards long. The petioles of these leaves are adhesive. By folding themselves one over another, and successively drying up, they grow into a stem which sometimes attains the dimensions of the trunk of an ordinary tree (about seven feet) and the stature of twelve to sixteen feet, and which is traversed throughout its centre by a stalk springing from the bulb. This stalk rises again several inches above the terminal leaf, then bends, sinks towards the ground, and terminates in a stem which carries at its extremity the male flowers, and at its base the female flowers, then the fruit. The latter, collected in clusters of twelve to fourteen, are elongated, of a prismatic triangular form, enveloped in a rind, green at first, then yellow, and internally consist of a soft, feculent, sugary pulp, very nutritious, and agreeable to the taste.

In its native clime the banana is born, grows, flourishes, fructifies, and dies in the space of twelve or eighteen months. In the climates most akin to ours, and in our European gardens, its development is not only on a smaller scale, but occupies a longer period, and it has been known to reach the age of ten or a dozen years.

enlarge-image
The Banyan Tree (Ficus Indica). 
The Banyan Tree  (Ficus Indica ).

By the side of these weak-stemmed plants, with their soft and  spongy contexture, grow hosts of robust trees, whose timber is compact and sometimes exceedingly hard, and whose branches are of immense span. My readers will probably remember the lines in which Southey so admirably describes one of the most majestic and most singular of these: the Banyan, or Indian Fig-tree (Ficus Indica ),[161] also designated the “Multiplying Fig-tree,” the “Admirable Fig-tree,” and “Tree of Life.” The passage will bear transcription:[162]

“It was a goodly sight to see
That venerable tree,
For o'er the lawn, irregularly spread,
Fifty straight columns propped its lofty head;
And many a long depending shoot
Seeking to strike its root,
Straight, like a plummet, grew towards the ground.
Some on the lower boughs, which crossed their way,
Fixing their bearded fibres, round and round,
With many a ring and wild contortion wound;
Some to the passing wind, at times with sway
Of gentle motion swung;
Others of younger growth, unmoved, were hung
Like stone-drops from the cavern's fretted height.
Beneath was smooth and fair to sight,
Nor weeds nor briars deformed the natural floor;
And through the leafy cope which bowered it o'er,
Came gleams of chequered light.”

The Banyan surpasses in diameter the finest oaks of Europe, and throws off numerous branches, of which several redescend towards the earth, force their way into it, take root therein, and in their turn develop into new trunks, whence spring other boughs that go through the same process of fructification; so that a single stem spreads in time into a kind of forest, and the canopy formed by the outgrowth of a solitary tree will frequently overshadow an area of 1700 square yards.

The evergreen foliage of this beautiful tree forms an immense vault, which has justly been compared to the domed roof of a stately edifice supported by a host of columns. Here a myriad birds raise their songs of joy; underneath, the weary pilgrim finds a delightful asylum; from branch to branch leap the mocking ape and the nimble squirrel. The Hindus hold their “Pagod tree” in great veneration. It is to them one of the emblems of their god Siva, and in its dense deep shade they assemble to celebrate their sacrificial rites, whether in honour of this potent deity, or whether in honour of Ganesha, a rural divinity, analogous in his attributes to the Pan of the Greeks and Latins.

Several other tropical trees possess, like the banyan, the property of producing adventitious roots which spring from the trunk or branches which implant themselves in the soil; but not one enjoys an equal power of reproduction and multiplication.

 

One of the greatest trees of southern Asia, and possibly one of  the greatest in the world, is the Teak or Indian Oak (Tectona grandis ), which covers vast areas of ground in Hindostan. It flourishes also in Pegu, Ava, Siam, Java, and the Burman Empire. It works easily, and though porous, is permanent and strong; is readily seasoned, and shrinks but little; is of an oleaginous character, and therefore does not corrode iron. It is as strong as oak, and more buoyant. Its durability is more uniform and decided; and to insure that durability it needs less care and preparation; for it may be taken into use almost green from the forest, without danger of dry or wet rot. It will endure all climates and all alternations of climate.[163]

The teak of Malabar, grown on the high table-lands in the south of India, is esteemed the best, because it is the heaviest, the most durable, contains the most oil, and is the closest in its fibre. Next in quality ranks that of Java, and inferior to these in some respects is the teak of Burmah, Rangoon, and Siam; which, however, is the most buoyant, and the best fitted for masts and spars.

African teak, let me note, is not teak properly so called, but the timber of the Oldfieldia Africana. It is largely imported from the west coast of Africa, and though an useful wood, lacks the most valuable properties of the genuine teak.

The teak is a handsome and even stately tree, often attaining the noble stature of 130 to 150 feet, with a trunk of proportionate diameter, upright, well-shaped, and surmounted by wide-spread branches. Its large leaves are oval, of a velvety under-surface, and besprinkled on the upper with whitish spots. Its flowers cluster at the extremity of the branch in an ample and beautiful panicle. The poisonous properties of its wood preserve it from the attacks of vermin, but render it dangerous to work, for men who are but lightly wounded by its splinters die after a very brief interval.

A less useful timber than the teak, but much esteemed for the manufacture of articles of luxury, is furnished by the Diospyros ebenum  and the Santalum album.

In the Flora of tropical Asia a very important position is occupied by the Laurel family. Several species of this family deserve to be particularized on account of their commercial value: thus, from the Laurus camphora  comes the camphor most esteemed by British physicians, while the aromatic rinds of the Laurus cinnamomumCulilawanMalabathrum, and Cassia, constitute the various kinds of cinnamon. The Laurus cassia  is not to be confounded with another Indian tree, one of the Leguminosæ, the Cassia fistula, whose enormous cods formerly played an important rôle under the name of Cassia in therapeutic science. While speaking of trees which produce aromatic substances, I must not forget to mention the Styrax benzoïn, and the Boswellia serrata. The former is a member of the family Styracaceæ, whose trees or shrubs, chiefly tropical, are known by their monopetalous flowers, their epipetalous stamens, their long radicle, leafy cotyledons, and by a part at least of the ovules being suspended. The Styrax benzoïn, a native of the Indian islands, yields the resin called benzoin. The juice exudes from incisions made in the bark, and when dried, is removed by a knife or chisel. Each tree yields about three pounds' weight annually, the gum formed during the first three years being superior in quality to that which subsequently exudes. It is largely employed by perfumers, and in medicine is esteemed a remedy for chronic pulmonary disorders. Styrax officinale, a native of the Levant, furnishes the balsamic resinous substance known as storax, which is also one of the materials manipulated by perfumers, and in medicine is used as a stimulating expectorant.

The Boswellia serrata  supplies the fragrant incense whose vapours were anciently supposed to be peculiarly agreeable to the gods made by man's hands or conceived by his imagination.

India is also the native country and home-land of the Indigo plants (Indigofera tinctoria, and Indigofera anil, of the Leguminosæ family), and the Gossypiums, from whose expanded fruits is obtained the all-powerful cotton; and in Cochin-China we meet with the Croton sebiferum  or Stillingia sebifera  (family of the Euphorbiaceæ), whose berries contain a rich concrete substance called “tree-tallow,” employed, in the far East, in the manufacture of tapers. The latter tree, popularly known as the “Tallow Tree,” has rhomboid leaves, with two prominent glands at the point of attachment between the stalk and the leaf; and its flower catkins are from two to four inches long. “Its fruits contain three seeds thickly coated with a fatty substance which yields the tallow. This is obtained by steaming the seeds in large caldrons, and then bruising them sufficiently to loosen the fat without breaking the seeds, which are removed by sifting. The fat is afterwards made into flat circular cakes, and pressed in a wedge-press, when the pure tallow exudes in a liquid state, and soon hardens into a white brittle mass. This tallow is very extensively used for candle-making in China; but as the candles made of it become soft in hot weather, they generally receive a coating of insect wax. A liquid oil is obtained from the seeds by pressing. The tree yields a hard wood used by the Chinese for printing blocks, and its leaves are employed for dyeing black.”[164]

Climbing and epiphytous [165] plants are very numerous in India; but there are none, perhaps, which in vegetative force and tenacity can be compared to those of the Calamus, and particularly of the Calamus rotang  (family of the Palmaceæ). These Lianas are all remarkable for their flexible stem, which attaches itself to the trees, and frequently attains the prodigious length of 200, 250, 300, and even 350 yards. This stem is formed of a series of internodes, or jointed pieces, more or less wide apart, each of which bears a leathery flower, with elongated sheath. The Calami frequently render the forests which they inhabit virtually impenetrable, through their long, flexible, and tenacious arms, stretching across from tree to tree, or crawling over the ground, and bristling with formidable thorns. It is these stems which are imported into Europe as bamboos, cut into different lengths, and there employed for various industrial purposes.

But it is time we took our leave of India, and allowed “observation with extensive view” to survey the far-spreading African forests. There, in the first place, we are called upon to salute the patriarch of the tropical Flora, the Baobab  (Adansonia digitata ), a gigantic genus of the family Bombaceæ.

enlarge-image
1. Baobab. 2. Elæis Guinensis, or Guinea Palm. 3. Acacia
verek. 
1. Baobab.  2. Elæis Guinensis, or Guinea Palm.  3. Acacia verek.

This colossus of the vegetable world was discovered in Senegal by the French botanist Adanson, in 1749. He measured the trunks of several individuals, and found them from 65 to 78 feet in circumference, with mighty branches, each of which was equal to a great oak or magnificent chestnut. One baobab he computed at 90 feet in girth, and its rounded crest extended over an area of upwards of 170 yards in circuit. A root which was exposed to view, through the  washing away of the superjacent soil, measured 110 feet in length. Adanson estimated the age of some of these Anakim of trees at 1500 years. They were just shooting above the ground, if this reckoning be true, at the time that Constantine, the first Christian emperor, removed the seat of empire from Rome to Constantinople.

There are other gigantic trees in the forests of Senegambia, as, for instance, the Khaya Senegalensis, which rears its crest to a height of 50 or 60 yards, whose hard reddish-coloured timber belongs to the species known in commerce under the name of Mahogany. Another kind of mahogany, but less valuable, called Senegal Mahogany, is furnished by the Swietenia Senegalensis (family of Meliaceæ, tribe of Cedrelaceæ), named after Baron von Swieten, a Dutch botanist. It forms a stately tree, some 60 or 80 feet high. Swietenia Mahogani, a native of the warmer regions of America and the West Indies, yields the mahogany of commerce. The first discovery of the existence of this kind of wood is ascribed to the carpenter on board Sir Walter Raleigh's vessel, when lying off Trinidad in 1595. It is not considered to reach perfection under the venerable age of two hundred years. The seeds prepared with oil are used by the modern Mexicans, as they were by the ancient Aztecs, for cosmetic purposes; and the bark is considered a febrifuge.

Among the most curious trees of the Senegal, whose Flora has quite a character of its own, travellers have singled out the Butter Tree (Bassia butyracea, family of the Sapotaceæ), whose fruits contain an edible fatty substance, used by the natives as a substitute for butter; and the Henna (Lawsonia inermis ), which also flourishes on the eastern coast and in Upper Egypt. The henna is a shrub from six to seven feet high. Its flowers exhale a goat-like odour, which seems much affected by the Orientals and the natives of Africa. Its roots, of a deep red hue, are distinguished by a bitter taste and astringent properties. Finally, its leaves supply an orange-red colouring matter, with which the Arabs and negroes tint their hair, beard, and nails.

Let us not pass over without the tribute of our respectful notice  the numerous tribe of Acacias, which form vast forests in the districts north of the Senegal, and yield the gum-arabic of commerce. The best known species of this important and useful group are the Acacia Arabica, or Red Gum-tree, the Acacia Adansoni, the Acacia vera, and the Acacia verek.

We also meet at Senegal with a tree which I ought, perhaps, to have ranked of right among those of India, and which, like many others, belong rather to the whole zone of the Tropics than to any particular country; I refer to the Tamarind (Tamarindus Indica ),[166]whose well-known name is supposed to be derived from the Arabic Tamar, signifying “dates,” and Indus, in allusion to its original habitat. There is only one species of the genus, but the East Indian variety has long pods, with six to twelve seeds, while the West Indian has much shorter pods, containing one to four seeds. It is a tree of graceful appearance, with elegant pinnated foliage and numerous racemes of fragrant flowers. The pods are slightly curved, and consist of a brittle brown shell, enclosing a soft, acid, brown pulp, traversed by strong woody fibres; a thin membranous covering wraps up the seeds. The pulp has a savour at once acid and sugary, and acts as a gentle laxative. The timber is useful for building purposes, and furnishes excellent charcoal for the manufacture of gunpowder.

The Sterculiaceæ have numerous representatives at the Senegal. These tall and handsome trees remind the traveller in their appearance of our English oaks. The seeds of the Sterculia acuminata  and tomentosa  are masticated by the negroes until reduced to a fluid paste, in which form they employ it to dye their cotton-stuffs yellow. The dye is very bright, and, it is said, extremely durable.

We know that a great part of the Gaboon is occupied by virgin forests, where Fig-trees are predominant, and in marshy soils the Mangle or Mangrove trees (Rhizophora mangle ), which must not be confounded with the savoury-fruited Mangoes of Eastern India. The Mangroves form, in the family of the Rhizophoras, a genus distributed  in the moist localities of the Tropics, and we shall hereafter meet with them in South America.

Equatorial Africa possesses several species of Palm-trees peculiar to it. Such are the Thorny Date-tree, the Borassus  of Ethiopia, the Raphia vinifera  of Congo, which, as its name “wine-bearing” indicates, furnishes a wine analogous to that extracted in other regions from other trees of the same family; the Elæis Guinensis, or Guinea Palm, whence we obtain the well-known product of palm oil. This oil, or palm-tree butter, forms an important article of food among the Guinea negroes. It is imported into Europe in large quantities, and employed in the manufacture of soap.

The forests of the Hottentot and Bechuana countries, and in general of all those regions bordering on the Cape Colony, are frequently of great extent, but mainly composed of trees of small stature, or even of shrubs, such as the Cape Olive, a few Acacias, some Compositæ and Conifers. Forests, as I have said, are rare in the explored portions of the west African coast; they become denser and more numerous as we leave the great ocean in our rear, and penetrate into that vast interior which for ages has been haunted by so many mysteries. Their Flora, however, offers no special character, and does not materially differ from that of Guinea and Senegambia.


[158] Matthew Arnold, New Poems: “Empedocles on Etna,” p. 16.

[159] F. de Lanoye, “L'Inde Contemporaine,” c. 1 er.

[160] Order, Musaceæ.

[161] Order, Moraceæ.

[162] Southey, “Poetical Works”—The Curse of Kehama.

[163] Craufurd, “The Eastern Archipelago.”

[164] Brande, “Dictionary of Science, Literature, and Art,” iii. 610.

[165] From the Greek ἑπι, upon, and φὑτον, a plant.

[166] Order, Leguminosæ.

Vegetable Life in the Forests of the New World

N ATURE , said Linné, is admirable above all in the smallest things: Natura maxime miranda in minimis. He might, perhaps, have more justly said, Natura non minus miranda in minimis quam in maximis : Nature is not less wonderful in the least than in the  greatest. Whether any created thing occupies a more or less considerable space, or contains a greater or lesser quantity of matter, is of no importance to the naturalist, who only studies the structure of the organs, the springs of life, and the different forces which set them in motion; and considered from this point of view, a vibrio [169] and an elephant, a penicillium and a baobab, possess for him the same importance, the same amount of interest. It would, however, be unjust not to recognize the fact that there is something very legitimate in the kind of reverential admiration which every man is conscious of in the presence of those things that symbolize, to a certain extent, power, strength, majesty, endurance—of those that possess in a high degree the two valuable qualities of force and greatness. Coleridge tells us that we admire the cataract because it is the type of power. Probably our feelings for the oak are connected with its emblematic properties of permanency, vigour, and durability. All the logic of logicians, and all the sentiment of natural philosophers, will never induce the mass of men to regard with the same interest an ant and a lion, a tuft of moss and a forest of oaks, a grain of sand and an Alpine peak. I do not think, therefore, that I am stooping to a merely vulgar prejudice in signalling out to the reader, among the vegetables of the forests, those whose exceptional dimensions and venerable antiquity are for every traveller an object of astonishment and curiosity. The truth is, that from their contemplation we derive a more vivid conception of Almighty Power than from the examination of even the most wonderful microscopical mechanism. To the still small voice of Nature our ears are deafened by the clash and clang of an ever-active world; but we cannot refuse to listen to the roar of the ocean or the reverberation of the thunder. As we move swiftly onward in the press of the crowd and the race of life, we ignore the tiny blade and the delicate organism beneath our feet; but our eyes  must perforce be opened to the splendours of the sea, the undulating summits of snow-crowned mountains, the sapphire vault of the starry heavens. Those things realize to us, at once and with impressive force, the ubiquitous majesty of the Divine Builder. And it is well that they should lift us for a while above the materialism of our daily lives into a purer atmosphere of thought and feeling—should bid us, while still lingering in the dusty track, expand our souls to hear

“The mighty waters rolling evermore.”

It is not only in tropical regions that we meet with the giants of the vegetable world. Europe possesses a few of them; isolated, it is true, but comparable in their stature to the most robust denizens of the Torrid Zone: such are the chestnut-tree of Etna, and the plane of Boudjoukdéré, near Constantinople, of which so many travellers have spoken. The remains of the virgin forests of North America also abound in species analogous to our own, and capable of attaining, with an almost incalculable longevity, truly extraordinary proportions.

 

The lofty table-lands of California (the Rocky Mountains) nourish an entire tribe of gigantic Coniferæ, frequently assembled in immense forests. The Pinus Lambertiana, the Pinus Sabiniana, and the Pinus insignis, are not less than 160 to 180 feet in height; the Douglas Fir  boasts of an almost equal stature, with a circumference which varies from 18 to 36 feet. Yet these colossal trees are surpassed by the Sequoia sempervirens, which is 240 to 260 feet high, and by the Titan of Titans, the huge Wellingtonia gigantea, which is also a Sequoia. I shall mention a few individuals of the latter species, whose dimensions may defy all comparison with the greatest trees of the Tropics.

According to Müller, about ninety-four of these Coniferæ flourish on a plateau of the Sierra Nevada, at an altitude of 5400 feet. They are distributed in small groups over a fertile soil. The gold-seekers have named one of them the “Miner's Cabin.” Its trunk, 320 feet in height, presents an excavation 16 feet in width. The “Three  Sisters” are individuals springing from one root; the “Old Bachelor,” stripped of its branches by successive hurricanes, stands in solitary desolation; the “Family” consists of two aged trees around which four-and-twenty scions have sprung up. The “Riding-School” is an enormous hollow trunk, prostrate on the ground, into which a man on horseback may enter as far as thirty yards. Another hollow trunk has been exhibited at San Francisco, where they have constructed out of it a saloon, adorned with tapestry and furniture, capable of accommodating forty persons.

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1. Large-leaved Magnolia. 2. Virginian Catalpa. 3. Pinus Sabiniana. 
1. Large-leaved Magnolia.  2. Virginian Catalpa.  3. Pinus Sabiniana.

Other resinous trees of smaller dimensions grow in the more or less humid localities of North America; such are the Chamœcyparis Chamæcyparis sphæroidea, which does not exceed 80 feet in height, and the Western  Thuya  of pyramidal outline. Nor must I forget to name, among the Conifers of this continent, the Cypress of Louisiana, a tree of handsome appearance, about 100 feet high and 12 to 15 feet in circumference, which lives, it is said, 5500 to 6000 years. Its leaves are shrunken like those of the larch; and from its roots, somewhat deeply buried, spring several protuberances, or rounded conical exostoses, which sometimes grow to the height of three feet without bourgeoning.

The forests of the West and of the South which have hitherto escaped the torch and the axe of the pioneer present to the traveller's admiring gaze those magnificent species described so eloquently by Chateaubriand and Cooper, and which are even less remarkable for their gigantic stature than for the majestic elegance of their port, the beauty of their foliage, and the dazzling splendour of their flowers. Some of these forests are partly formed of Oaks whose leaves assume in autumn a purple tint, like the “pupureum lumen” of the Latin poet. In others the dominant trees are the Plane of the West, the Maple, the round-crested Tulip, the large-leaved Catalpa, the Magnolia with white and scented blossoms. To their trunks clings a whole world of climbing, creeping, and parasitic plants; as the Virgin Vine, the Sumach, and the Virginian Jasmine.

Mexico, as far as relates to its climate and productions, has been divided into three distinctly marked regions, defined not by latitude, but by the elevation of various portions of its territory. The upper region, or Cold Lands, is that of the lofty mountains; the mean region, or Temperate Lands, that of the intermediate plateaus; the inferior region, or Hot Lands, is that of the low plains, sometimes arid, sometimes marshy or wooded.

The arborescent Flora of the first two regions very nearly approximates to that of our northern countries; it principally consists of Pines, Firs, Oaks, and Arbute Trees. But in the Hot Lands the vegetation generally assumes, as we descend towards the south, all the characteristics of the tropical Flora. The feathery and graceful Palm trees re-appear, mingled with Coryphas, Oreodoxas, Malpighiaceæ, and Bignoniaceæ. There also grows the Crescentia cujete, or Calabash-tree, which is likewise found in the Antilles; it has a tortuous trunk, long branches extended horizontally, and ovoid fruits, clothed with a hard woody bark, which the Indians fabricate into vessels of divers forms, painting them in the liveliest colours.

Mexico is the country of the Morus tinctoria  and the Hæmatoxylon Campechianum. These two trees furnish the dye-wood which forms so important an article of commerce: the first, under the name of the “yellow wood of Tampico” or “Tuspan;” the second, under that of “Campeachy wood.” It is in the hottest and most humid parts of the southern provinces of this Republic that we meet, for the first time, with one of the most precious trees of the Equinoctial Zone, the Cacao-tree (Theobroma cacao ), whose bruised and roasted seeds, mixed with variable amounts of sugar and starch, form the different kinds of Cocoa; or, sweetened and flavoured with vanilla or other substances, the article known as Chocolate. It is but a small tree, with large entire leaves, and clustered flowers growing from the sides of the old stems and branches. Its large pentagonal fruits vary from six to ten inches in length and three to five in breadth, and contain between fifty and a hundred seeds.

The Vanilla planifolia, another Mexican native, famous for its succulent fruit, is a plant of the Orchidaceous order, which climbs about other trees in the manner of ivy. It is the only genus of the family which possesses any economical value. The delicate perfume of its fruit is due to the presence of benzoic acid, which forms in crystals upon the pod, if left undisturbed.

 

Already, in Central America, we encounter the first ranks, the vanguard, as it were, of those vast impenetrable forests which spread over the whole northern region of South America to the banks of the Amazon, and cover with dense foliage immense areas in Guiana and Brazil. If we would pause again to wonder at the Giants of the Vegetable Kingdom, we shall find many well worthy of our consideration. Such, for example, is the Bertholletia excelsa, a colossal Lecythidacean  on the borders of the Orinoco, whose large fruits are known in Europe as “Brazil nuts,” the seeds being enclosed in large woody vessels. The Sapucaya (Lecythis ollaria ) is scarcely less abundant, and of immense height. Its fruit, popularly called “Monkey's Drinking-cups” (Cuyas de Macaco), consists of a cup-like vessel, with a circular hole at the top, in which a natural lid fits neatly. When the nuts are ripe this lid becomes loosened, and the heavy cup falls with a crash, scattering the nuts over the ground.

“What attracted us chiefly,” says a traveller in the virgin forests,[170] “were the colossal trees. The general run had not remarkably thick stems; the great and uniform height to which they grow without emitting a branch, was a much more noticeable feature than their thickness; but at intervals of a furlong or so a veritable giant towered up. Only one of these monstrous trees can grow within a given space; it monopolises the domain, and none but individuals of much inferior size can find a footing near it. The cylindrical trunks of these larger trees were generally 20 to 25 feet in circumference. Von Martius mentions having measured trees in the Parà district belonging to various species (Symphonia coccinea, Lecythis spirula, and Cratæva Tagia), which were 50 to 60 feet in girth at the point where they become cylindrical. The height of the vast column-like stems could not be less than 100 feet from the ground to their lowest branch. Mr. Leavens, at the saw-mills, told me they frequently squared logs for sawing 100 feet long, of the Pas d'Arco and the Massaranduba. The total height of these trees, stem and crown together, may be estimated at from 180 to 200 feet: where one of them stands, the vast dome of foliage rises above the other forest trees as a domed cathedral does above the other buildings in a city.

“A very remarkable feature in these trees,” says Mr. Bates, “is the growth of buttressed-shaped projections around the lower part of their stems. The spaces between these buttresses, which are generally thin walls of wood, form spacious chambers, and may be compared to stalls in a stable: some of them are large enough to hold  half-a-dozen persons. The purpose of these structures is as obvious, at the first glance, as that of the similar props of brickwork which support a high wall. They are not peculiar to one species, but are common to most of the larger forest trees. Their nature and manner of growth are explained when a series of young trees of different ages is examined. It is then seen that they are the roots which have raised themselves ridge-like out of the earth; growing gradually upwards as the increasing height of the tree required augmented support. Thus they are plainly intended to sustain the massive crown and trunk in these crowded forests, whose lateral growth of the roots in the earth is rendered difficult by the multitude of competitors.”

Scarcely less remarkable, and certainly not less useful, than the Traveller's Tree of Madagascar is the Massaranduba, or Cow Tree, of these grand Brazilian wildernesses. It is one of the largest of the forest monarchs, but rather reminds you of monarchy in its decay than of regal pomp, owing to its deeply-scored reddish and ragged back. A decoction of this bark is used as a red dye for cloth. The copious milk-like fluid which the tree supplies, and which may even be drawn from dry logs that have stood for days in the sun, is wholesome and nutritious, if taken in moderate quantities. On exposure to the air it soon thickens into an excessively tenacious glue.

But, apart from these monstrous trees, the virgin forest possesses an abundance of interest for even the least observant traveller, while in its various phases it is adapted to astonish, to impress, and to awe a thoughtful mind. It is true that it does not boast of that profusion of floral ornament, of those gay and exquisite buds and blossoms, which make the charm of our English woods; but in its infinite variety of foliage the grace of colour and beauty of form are ever present. What most seizes upon the soul, however, is its intense silence—which the occasional scream of some wild animal, or the infrequent song of some pensive bird, or the sudden crash of some over-toppling tree, does but render the more significant and appalling. The hush is like that  which prevails on a battle-field before the dread voices of the cannon speak of death and carnage, but, unlike that hush, it is never interrupted. Morning comes with its cold gray lights, noon with its warmth and radiance and splendour, night with its orbed moon and pearly dews, but the hush still reigns undisturbed, and it seems to the traveller as if it would never be broken but by the sounds which shall proclaim the end of all things!

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1. Blechnum Brasiliense. 2. Alsophila horrida. 3. Panicum plicatum.
4. Marauta. 5. Caladium violaceum. 
1. Blechnum Brasiliense.  2. Alsophila horrida.  3. Panicum plicatum.
4. Marauta.  5. Caladium violaceum.

It is rather by the varied characteristics of the species which compose it, by their fantastic structures and useful properties, than by its gigantic outcomes, that the wild flora of these forest-regions appeals to our admiration. We are struck at first by the infinite variety, richness, and elegance of the vegetable forms. Especially do we pause in wonder before those glorious Tree-Ferns which I take to  be the finest growth of the tropical wilderness. These Ferns, from 36 to 50 feet in height, are not unlike Palms in their physiognomy; their stem is only less upright, shorter, and more scaly; their foliage, slightly dentated on the edges, is more delicate, of a looser and more transparent texture. To this family belong the Blechnum Brasiliense  and the Alsophila horrida. Not less attractive in appearance are the Clusia rosea  or the Carolinea insignis. The former of these trees belong to a family (that of the Clusiaceæ) nearly all whose representatives throw off from every point of their branches long aerial roots. The traveller reposes with a feeling of Sybaritic delight under its thick and evergreen foliage, enriched with brilliant flowers. The second, with its shrunken leaves, owes the specific epithet (insignis, “remarkable”) which botanists have imposed upon it, to the peculiar structure of its flowers. The latter bear in the centre of their chalice a great number of stamens, which form a silken tuft of the most graceful design.

The Gramineæ, like the Ferns,—to use an expression of Humboldt's,—“ennoble themselves” under the Tropics: witness the Bamboo, the Sugar-Cane, the Sorgho, and the great Panicums. Of the latter genus we have already seen in Africa numerous species. America in its turn offers to our attention the Panicum maximum  and plicatum, wood-inhabiting Gramineæ, which without attaining to the dimensions of the bamboo, or even to that of the cane, far surpass that of their European congener, the millet.

The graceful palms abound in South America. The greatest of all, the Cocoa-tree, seems there to have discovered its true home, for it nowhere else acquires a greater development. There, too, the Banana flourishes marvellously, no less than the Cocoa-tree, in a wild state, and, like the latter, is carefully cultivated on account of its nourishing and savoury fruits. A multitude of lianas and epiphytous plants twine round the trunks and branches of the trees, and frequently choke up their failing life. Some are indigenous to all tropical countries: the Calamus Rotang, for example; others are more particularly, or even exclusively, proper to the New World.

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1. Banana. 2. Carolinea insignis. 3. Clusia rosea. 
1. Banana.  2. Carolinea insignis.  3. Clusia rosea.

The family of Aroideæ is there represented by the Pothos, whose fleshy and herbaceous stems are surmounted by leaves sometimes arrow-headed, sometimes digitate or elongated, and always divided by thick cord-like nerves. We know that the Aroideæ alone possess, in the vegetable kingdom, the property of disengaging, while flowering, a heat appreciable by the thermometer. To this family belong the Caladiums, a genus closely allied to the Pothos. With these lianas mingle the branching stems of the Passifloræ, or Passion-Flowers, so named because Pierre de Ceza, in his “Histoire du Pérou,” asserted that he had recognized in the fantastic flowers of this genus of plants all the instruments of our Saviour's Passion—an idea which could only have been conceived by an imaginative and credulous Spaniard. Elsewhere the Bignonias open by hundreds their large and richly-coloured flowers; the Bauhinias stretch along the trees their long leafless branches, often 40 to 45 feet in length, which sometimes hang vertically from the lofty summits of the Swietenias, or Mahogany trees, and sometimes extend obliquely from one huge trunk to another, like the ropes of a ship. The Tiger-Cats, says Humboldt, display a wonderful agility in mounting or descending these graceful vegetable shrouds.

Upon the umbrageous banks of the Rio Magdalena grows a creeping Aristolochus, whose flowers in their extraordinary development surpass those of the Rafflesia Arnoldi, measuring often three feet and a half in circumference. The forests of which we are now speaking also nourish numerous species of Convolvulus; I may particularize the Convolvulus batatas, a climbing plant, whose roots produce the feculent and saccharine tubercules known over the wide world by the name of “Patates,” and frequently but erroneously confounded with that most useful vegetable, the Potato. The root of another Convolvulus, a native of Mexico, constitutes the Jalap officinalis, which figures in the veterinary pharmacopœia as an important purgative.

Certain lianas, common enough in the South American forests, belong to the family of Sapindaceæ, which, like the orders Loganiceæ and Euphorbiaceæ, owe their reputation chiefly to the medicinal or poisonous substances extracted from them. Among the Sapindaceæ I shall mention only the genus Paullinia, which includes several species endowed with narcotic properties. These properties appear especially developed in the Paullinia pinnata. Its bark, leaves, and fruit contain an abundant acrid principle with which the Indians of Brazil prepare a slow but certain poison. The Indians of Guiana extract from the Paullinia cururu  another substance with which they envenom their arrows, and which was long supposed to be the veritable Wourali. But Sir Richard Schomburgk has shown that the latter formidable poison is really extracted, as I have already recorded, from the Strychnos toxifera, a shrub of the family Loganiaceæ, which flourishes in Guiana and Brazil. To the same family and  the same countries belong the Ignatia amara, whose seeds are known by the name of “St. Ignatius' Beans.” These beans contain two alkaloids, Strychnine  and Brucine, which we also extract from the Nux vomica, and which must be classed among the most violent poisons known to the toxicologist.

While speaking of the poisonous plants of South America, a few words in reference to the Manchineal (Hippomane Mancenilla ) will not be inappropriate. This tree thrives best, it is said, on the sea-shore. It bears a profusion of very pretty fruit, resembling in colour and form the Red Apple (the Spanish Manzanilla ), and exhaling an agreeable, lemon-like odour. They are, therefore, scarcely less beguiling than Dead Sea fruits; but they are also very poisonous, yet less deadly than the milky juice which flows from the slightest incision made in the tree's thick and grayish bark. This juice, received into the stomach, or introduced into the blood through a wound, slays the victim with awful quickness. If it do but touch the skin, it excites a violent irritation, and raises swellings or boils of the worst description. The very vapour which it emits causes a painful itching in the eyes, the lips, and the nostrils. It was formerly asserted that to sleep under the shade of a Manchineal tree was certain death; but the naturalist Jacquin, in the interests of science, courageously made the experiment, and proved the falsity of the story.

The Manchineal is not unfrequently confounded with other poisonous Euphorbiaceæ, as the Sapium aucuparium  and the Excœcaria agallochia, which flourish in very nearly the same regions. The Excœcaria, it is said, is not less dangerous than the Manchineal. It owes its name (ex, and cœcus, “blind”) to the circumstance (or the fable) that some European sailors, while felling wood in the forest, having accidentally struck with their axe a tree of this species, were blinded by the milky juice which sprang into their eyes.

By a kind of compensation, the Tropical Forests, which contain so many poisonous plants, produce also a great number of the highest utility to man. Some offer him efficient remedies against the diseases which beset his frame; others nourish him with the fecula  of their roots or the delicious substance of their fruits; others again supply him with textile fibres, dyeing or resinous materials, and woods which the artist and the artisan convert to numerous uses. This vegetable wealth has been widely distributed over South America. It will suffice to indicate a few of its more notable sources.

If we direct our attention to medicinal plants, we shall probably find none more precious than the Quinquina, whose bark is the most effective of all febrifuges, and which is endowed, moreover, with very valuable tonic and depuratory properties. Sir Samuel Baker, in his recent address to the British Association at Dundee, pronounced it the traveller's best friend, the powerful weapon with which he could securely enter the African wilderness, and successfully contend against its demon-host of fevers and agues. The Quinquinas (genus, Cinchona ; family, Rubiaceæ) are trees or evergreen shrubs with large and handsome leaves, and flowers whose form and fragrance remind one of the lilac. They are diffused over the two slopes, but chiefly along the eastern slope, of the Andean Cordilleras, in the republics of Venezuela, New Granada, Ecuador, Peru, and Bolivia. The traveller meets them occasionally in picturesque groups or thickets which the Peruvians call Manchas  (spots); but they are more frequently scattered in immense forests.

What of the lactiferous and resinous plants? South America is the native land of the trees whence we extract the resinous gums called “Animé d'Amérique,” “White Amber,” and “Soft Brazilian Copal,” and the “Hevea Guyanensis,” which furnishes the greater portion of the caoutchouc imported into Europe.

Caoutchouc was described for the first time in 1736, by the scientific travellers Bouguer and La Condamine, members of a Commission despatched to Peru by the Parisian “Académie des Sciences,” to measure an arc of the meridian. A few years later, the engineer Fresneau, who resided for a long time in Guiana, collected, with the assistance of a native, ample information in reference to caoutchouc and the tree which produced it. Finally, in 1768, was found in a work by the traveller Aublet on the Flora of Guiana, the description  and figure of the Hevea. This tree attains a height of 50 to 70 feet. The almond enclosed in the kernels of its fruits is white, of a very agreeable taste, and much esteemed by the Indians, who also extract from it an oil for seasoning their food.

The Banana, the American Agave, the Bamboo, and divers Palm-trees supply the inhabitants of South America with suitable materials for the fabrication of various tissues, from the finest and most brilliant linen cloth to the rude mats which ornament the cabin of the savage. Trees bearing fruits or edible roots are innumerable. To the Bananas and Cocoa-trees which I have already mentioned, we may add, as the most useful, the Maranteas or Canneas, especially the Maranta arundinaceaM. alloya, and M. nobilis, whose roots, rasped and washed, constitute the popular and valuable farina so widely known as Arrow-root ; the Guavas (Psidium pyriferum, and P. pomiferum ), whose gilded fruits contain a succulent and perfumed pulp; the Papaw tree (Carica papaya ), resembling the Palm in its port and aspect, and also loaded with large yellowish fruit, whose flesh is exceedingly savoury and aromatic. The Papaw, moreover, enjoys some extremely remarkable properties; thus, its milky juice exhales, when burnt, an ammoniacal odour, and chemical analysis has recognized therein the presence of fibrine. Mix some of this juice in water, plunge into the mixture fresh hard meat, and in a few moments it will become exquisitely tender. The very exhalations of the tree operate in the same manner, and the inhabitants of the regions where it flourishes suspend to its branches such meat and poultry as they wish to soften.

 

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FLORA OF THE NEW WORLD.
1. Papaw Tree (Papaya Sativa)
2. Great American Cocoa-Nut Tree.
3. Mangrove (Rhizophora mangle). 
FLORA OF THE NEW WORLD. 
1. Papaw Tree (Papaya Sativa )    2. Great American Cocoa-Nut Tree.
3. Mangrove (Rhizophora mangle ).

The immense forests of Brazil and Guiana are for the whole world an inexhaustible storehouse of woods for dyeing and cabinet work. They spread their dense masses of foliage along the borders of the sea, where the Mangroves (Rhizophora mangle ) plunge their adventitious roots into the mud inundated by the surging tides of those regions, and form a kind of impenetrable palisade, behind which grow in infinite variety trees of the costliest timber. Such are the Swieteniæ, or Mahogany trees; the Ferolia Guyanensis, which supplies the well-known rose or satin wood; the Jacaranda Brasiliensis, and the Dalbergia, which yield the violet ebony; the Sterculia acuminata, whose flowers exhale a fœtid odour, and whose timber, called “stinkwood,” is nevertheless held in high esteem on account of its durability, the fineness of its texture, and the excellent polish of which it is susceptible. Nor must we forget the Cæsalpineæ, whose woods are impregnated with a red colouring matter which varies in tint according to the species, and which are largely employed by the dyer under the names of “Brazil wood” and “Pernambuco wood.” A great number of other woods which we procure from these countries, and which are in daily use in cabinet work, toys, marquetry, and dyeing, belong to vegetable species as yet undetermined. We might, however, almost venture to assert that whatever tree you accidentally and at haphazard struck down in these forests, either its timber, bark, or roots would be found capable of being utilized.

 

I have not mentioned, among the species proper to the Forests of the New World, those which are common with our own, and which abound upon elevated lands. The extraordinary height to which not only isolated mountains, but whole districts rise, in the vicinity of the Equator, and the low temperature which is the consequence of this elevation, provide the inhabitant of the Torrid Zone with a remarkable spectacle. For while, as Humboldt remarks, he may look around him upon groves of palms and bananas, he also sees those vegetable forms which are regarded as more particularly belonging to the countries of the North. Cypresses, firs, and oaks, barberries and alders, closely resembling our own, cover the table-lands of Southern Mexico and that part of the Andes which the Equator traverses. Thus Nature allows the denizen of the Torrid Zone to see, without quitting his native land, all the vegetable forms of the earth, at the same time that from one pole to the other the entire vault of heaven reveals to his gaze its luminous worlds.

I conclude my account of the South American Forests with a  picture taken from the interesting volume of Mr. Bates, and drawn on the bank of a forest stream flowing into the Murncupé. “A glorious vegetation,” he says, “piled up to an immense height, clothes the banks of the creek, which traverses a broad tract of semi-cultivated ground, and the varied masses of greenery are lighted up with the sunny glow. Open palm-thatched huts peep forth at intervals from amidst groves of banana, mango, cotton, and papaw trees and palms. Both banks are masked by lofty walls of green drapery, here and there a break occurring. The projecting boughs of the trees are hung with natural garlands and festoons, and an endless variety of creeping plants clothe the water frontage, some of which, especially the Bignonias, are ornamented with large, gaily-coloured flowers. Art could not have assorted together beautiful vegetable forms so harmoniously as is here done by Nature. Palms, as usual, form a large proportion of the lower trees; some of them, however, shoot up their slim stems to a height of sixty feet or more, and wave their branches of nodding plumes between you and the sky. One kind of palm, the Pashiúba (Iriartea Exorhiza ), which grows here in greater abundance than elsewhere, is especially attractive. It is not one of the tallest kinds, for when full-grown its height is not more, perhaps, than forty feet; the leaves are somewhat less drooping, and the leaflets much broader than in other species, so that they have not that feathery appearance which those of some palms have, but still they possess their own peculiar beauty.”

Probably there is no richer field on earth for the naturalist, the poet, or the artist than the virgin forest;—

“To mark the structure of a plant or tree,
And all fair things of earth, how fair they be!”


[169] The genus Vibris  is the type of a tribe of animalcules commonly known as microscopic eels, remarkable for their extraordinary minuteness. One species is parasitic upon wheat, and when full grown attains a quarter of an inch in length; but the young are so microscopically small that 30,000 might be contained in a single grain of wheat.

[170] H. W. Bates, “The Naturalist on the Amazons,” pp. 37-39.

The living plants may be divided into two grand divisions—Flowering Plants and Flowerless Plants—with five main subdivisions, according to the complexity and structure of their reproductive organs, or seed structure. The scientific names of these groups are the Thallophyta, the Bryophyta, the Pteridophyta, the Gymnosperms, and the Angiosperms.

Each of the five main groups is divided into a number of lesser subdivisions, sometimes called phyla, orders, each of which is composed of several families.

Most systematic botanists begin the study of plants with the lowest forms of plants and proceed to the highest. In the following classification, however, the usual order has been reversed  because of its greater interest for a large majority of readers; the highest division is placed first and the lowest last.

In the earlier days of the science of botany nearly every botanist's energies were devoted to this branch which we now call systematic botany. There are now named and described close on a quarter of a million of living species of plants altogether, including the lower and often nearly invisible forms, and of this vast number about one hundred and thirty thousand belong to the highest group of all—the Angiosperms. With nearly a quarter of a million described forms to deal with the value of such keys will be recognized.

Sub-Kingdom I.—Flowering Plants (Phanerogams ), or Spermophytæ.

(1) Angiosperms  (anj ´ĭ-o-sperms )—Plants producing protected seeds.

The greatest group, the Angiosperms, with over a hundred and thirty thousand species, contains nearly all the plants that yield crops of economic importance to man, or that decorate his gardens, or that feed his sheep or cattle. They have netted-veined leaves. When this group is further examined, there are found to be two well marked divisions—Monocotyledons and Dicotyledons. The first has embryos with only one cotyledon or “seed leaf,” the second has embryos with two. The Angiosperms include over one hundred and thirty thousand species, divided among sixty-two orders, only the most important families of which can be given here.

Order I.Ranunculaceæ: Herbs or small shrubs; about thirty genera.

Anemone  (windflower): Perennial herb. Dry copses. Massachusetts to New Jersey and west to Colorado.

Anemonella  (rose anemone): Open woods. Canada to Georgia and west through Mississippi Valley.

Caltha  (cowslip, marsh marigold): Perennial herb. United States and Canada.

Clematis  (virgin's bower): Perennial. United States and Canada.

Ranunculus  (buttercup, crowfoot): Herb, annual or perennial. Canada, United States and Europe.

Thalictrum  (meadow rue): Perennial herb. United States and Canada.

Order II.Berberidaceæ: Shrubs or perennial herbs; nineteen genera.

Berberis  (barberry): Fruit, a sour berry. Found in Europe; naturalized in New England.

Podophyllum  (May apple, mandrake): Perennial herb. Fruit, a berry. Found: Eastern North America; a species in Himalaya Mountains.

Order III.Papaveraceæ: Annual or perennial herbs with milky or colored juice; about twenty-four genera.

Papaver  (poppy): Geographical home on southern edge of North Temperate Zone, spreading north and south. Great opium districts are the valley of Ganges, Asiatic Turkey, Persia, Egypt, Asia Minor, China. From India, fourteen million pounds annually. Persia and Turkey, seventy-one million pounds.

Order IV.Cruciferæ: Herbs; about one hundred and seventy-two genera.

Brassica  (turnip, mustard, cabbage, cauliflower, rape): United States, Europe, India, Syria and Russia.

Capsella  (shepherd's purse): Naturalized in United States; from Europe.

Cochlearia  (horseradish): Perennial. Root. Middle and southern edges of North Temperate Zone, from Great Britain to Asia and northeastern America.

Isatis  (woad): Biennial. Throughout Europe. Cultivated in Azores and Canary Isles.

Nasturtium  (watercress): Europe and northern Asia. Cultivated in Palestine, Hindustan, Japan.

Order V.Capparidaceæ: Herbs, shrubs, trees; twenty-three genera.

Capparis  (caper): Small shrub. Southern France and Mediterranean countries, Sicily, Malta.

Order VI.Violaceæ: Herbs; twenty-one genera.

Viola  (violet): Perennial. Canada; United States, west to Colorado; throughout Europe, some parts of China, Japan, India.

Order VII.Biximæ: Shrubs; 29 genera.

Bixa  (arnotto): Tropical America. Cultivated in southern Europe, Burma, Philippine Islands, Hindustan.

Order VIII.Terustrœmiaceæ: Shrubs and small trees; thirty-two genera.

Thea  (tea): Shrub. China. Cultivated between parallels of 25° and 35° throughout Asia. In Kangra, Gurhwal, Assam, Cachar, Sylhet, Chittagong, Darjeeling, Chota, Nagpur, Hindustan, Japan, Australia, Jamaica, Brazil, North America.

Order IX.Malvaceæ: Herbs, shrubs.

Gossypium  (cotton): Tropical and sub-tropical. East Indies, China, Asiatic Islands, Greece, islands in eastern Mediterranean, Asia Minor, northern and western Africa, Australia, West Indies, southern United States, Venezuela, British Guiana, Brazil.

Order X.Sterculeaceæ: Trees and shrubs.

Theobroma  (cocoa): Tropical and sub-tropical. Brazil and north of Brazil, West Indies, Mexico. Cultivated in Philippine Islands, southern Europe, India.

Order XI.Tiliaceæ: Trees and shrubs; 40 genera.

Corchorus  (yellow jute): Southern belt of North Temperate Zone and Tropics. Cultivated in southern and western Asia, Grecian Archipelago, central and northern Africa.

Order XII.Linaceæ: Shrubs and herbs; 94 genera.

Linum  (flax): Herb. Widely distributed. Hindustan, southern Egypt, throughout Europe, southern and middle Russia, northeastern America.

Erythroxylon  (coca): Shrub. Tropical and sub-tropical. Bolivia, Peru, Ecuador, Colombia, northern Brazil.

Order XIII.Zygophyllaceæ: Trees, shrubs, herbs; seventeen genera.

Guaiacum  (lignum-vitæ): Tree. Tropical and sub-tropical. Exclusively American; native to West Indies.

Order XIV.Rutaceæ: Small trees and shrubs; eighty-three genera.

Citrus  (orange, lemon, shaddock): In all regions of no frost. India. Cultivated in Persia, Syria, southern Europe, northern Africa, Spain, China, Japan, Sicily, Australia, Brazil, West Indies, Florida, southern California, Azores.

Order XV.Meliaceæ: Trees; thirty-seven genera.

Swietenia  (mahogany): Large tree. Tropical and sub-tropical. West Indies, Bahamas, Central America, southern Florida. Cultivated in southern British India.

Order XVI.Iliciniæ: Trees and shrubs; three genera.

Ilex  (Paraguay tea): Small tree. Paraguay. In Parana, ten million pounds produced annually.

Order XVII.Rhamnaceæ: Trees and shrubs; thirty-seven genera.

Ceanothus  (New Jersey tea): Shrub. Eastern North America.

Rhamnus  (buckthorn): Shrubs, small trees. Southern Persia and southern Levant countries. Grows as far north as England.

Order XVIII.Ampelideæ: Woody vine; few genera.

Vitis  (grape): Zone from 21° N. latitude to 48°. British Isles and Portugal, east to Persia. Middle Atlantic States to California. Cultivated in Australia.

Order XIX.Sapindaceæ: Trees and shrubs; seventy-three genera.

Acer  (maple): Tree. Not south of 38° N. latitude, except in high mountains in northern United States and southern British America.

Order XX.Anacardeaceæ: Trees and shrubs; forty-six genera.

Anacardium  (cashew nut): Tropics of Asia and America, Jamaica.

Rhus  (sumach): North America, Canada to Gulf States; Arkansas, Levant, and western Europe, Syria. Cultivated in Sicily, Italy, Turkey, Spain, Portugal.

Order XXI.Leguminosæ: Herbs, shrubs, trees; four hundred genera.

Acacia  (gum arabic): Shrubs and small trees. Tropical and sub-tropical, but widely distributed. Australia, Africa, Asia, America.

Arachis  (peanut): Sub-tropical. Southern United States, southern and central Virginia, the Carolinas and Tennessee.

Astragalus  (gum tragacanth): Small shrub or herb. Sub-tropical. Persia, Greece, east Mediterranean Islands, Syria.

Cassia  (senna): Tropical and sub-tropical. Widely distributed.

Cæsalpinia  (Brazil wood): Trees. Brazil.

Dalbergia  (rosewood): Trees and vines. Brazil and southern Asia.

Glycyrrhiza  (licorice): Small shrub and herb. Italy and southern Europe, southern England. Cultivated in Spain and Portugal.

Hæmatoxylon  (logwood): Small tree. Yucatan, Guatemala, Honduras, Isthmus of Panama, West Indies. Cultivated in Burma.

Indigofera  (indigo): Shrub. India, Java, East Indies, north Africa, West Indies, Central Asia.

Lens  (lentil): Annual. Syria, Egypt, southern and central Europe, Hindustan.

Phaseolus  (bean): Annual herb. Tropics and Temperate Zones to forty-fifth parallels.

Pisum  (pea): Annual herb. Central and southern Europe, Egypt, Syria, Japan, India, China.

Tamarindus  (tamarind): Tree. Tropical and sub-tropical. Africa. Cultivated in Arabia, southern India, Ceylon, Java, Philippines, northern Australia, Pacific Isles, South America.

Order XXII.Rosaceæ: Trees, shrubs, herbs; seventy-one genera.

Fragaria  (strawberry): Herb. Widely distributed, even to Kamchatka and Alaska.

Prunus  (plum): Tree. Temperate Zone, south of 60°. Europe, western Asia. Cultivated in northeast America.

Prunus  (cherry): Tree. North Africa, Holland, Portugal. Cultivated in southeastern Africa, America, Belgium, England.

Prunus  (apricot): Tree. Armenia, Persia, China, Japan, California.

Prunus  (peach): Tree. Southern half of North Temperate Zone in Asia, Europe, America, New Jersey, Pennsylvania, Delaware, Maryland.

Pyrus  (apple): Tree. England, France, Germany, Netherlands, Prussia, Poland, United States, south Australia.

Pyrus  (pear): Tree. China, Syria, Persia, central and northern Europe, Belgium, France, Great Britain. Cultivated in North America.

Pyrus  (quince): Tree. Northern Persia, east and west. Cultivated in northeastern America, Portugal.

Rubus  (black raspberry and raspberry): Shrub. Temperate Zone, between 30° and 50° latitude. In North America, Europe north to sixtieth parallel, south to northern parts of Africa, Asia Minor, and eastward into India; also in British Isles.

Order XXIII.Saxifragaceæ: Shrubs, herbs; seventy-three genera.

Ribes  (currant): Shrub. Lapland and southern Europe; also in the New World, northern United States to south and middle Canada.

Ribes  (gooseberry): Shrub. France, England, Germany and northeastern Russia, Siberia.

Order XXIV.Combretaceæ: Shrubs, trees; seven genera.

Terminalia  (myrobalano): Large trees. Tropical India, along southern fringes of Ghaut Mountains, and in Burma.

Order XXV.Myrtaceæ: Trees; seventy-six genera.

Bertholletia  (Brazil nut): Large tree. Tropical South America, Panama.

Eugenia  (cloves): Molucca Islands. Cultivated in Brazil, West Indies.

Eugenia  (allspice): Jamaica.

Myrtus  (myrtle): Tropical and sub-tropical. Southeastern Italy. Cultivated in all Mediterranean countries.

Order XXVI.Lythraceæ: Tropical trees; thirty genera.

Punica  (pomegranate): Persia. Cultivated in Syria, Asia Minor, Levant, southern Europe, China, Japan, South and North America.

Order XXVII.Cucurbitaceæ: Herbs; sixty-eight genera.

Citrullus  (watermelon): Herbaceous vine. Africa. Cultivated in southern Europe and southern and middle North America.

Cucumis  (cucumber): Northeastern India. Cultivated in Levant, southern Asia, southern Europe, Africa, southern Russia, United States.

Cucumis  (muskmelon): British India, Baluchistan, West Africa, Guinea, banks of Niger. Cultivated in Mediterranean States, India, China, Japan, middle and southern United States.

Cucurbita  (squash): Annual. Europe and western Asia. Cultivated in Pacific Islands, southern Asia, Africa.

Cucurbita  (pumpkin): Warm climates.

Order XXVIII.Umbelliferæ: Herbs; one hundred and fifty-two genera.

Apium  (celery): Biennial. Great Britain, western Europe, Mediterranean shores, Peloponnesus, Caucasus, Palestine, South America, and western coast of North America to southern California.

Coriandrum  (coriander): Annual. Tartary. Cultivated in Hindustan, Burma, middle, southern and western Europe, North America.

Carum  (parsley): Biennial. Mediterranean countries and Asia Minor. Cultivated in Japan, England, and northeastern America.

Carum  (caraway seed): Lapland to Siberia. Cultivated in Great Britain and Continent south of 60°, North Africa, Hindustan, Burma, northeastern America.

Cuminum  (cumin): Northern Africa, middle and southern Europe, Syria, Hindustan, Bombay, Burma.

Daucus  (carrot): Biennial. Herb. All over Europe south of 60°, especially in France, Germany, northern Africa, southwestern Asia, China, Japan. Cultivated in North America.

Fœniculum  (fennel): Biennial. Levant. Cultivated in Hindustan, Atlantic States, France, Germany, Great Britain, southern Europe.

Pinipinella  (anise): Perennial. Egypt, Syria, Malta, Spain, southern Germany, Hindustan, Japan.

Pencedanum  (parsnip): Biennial. Europe, southern Greece. Cultivated in Asia and North America.

Ferula  (asafetida): Middle and western Asia.

Order XXIX.Rubiaceæ: Trees, shrubs, herbs; three hundred and thirty-seven genera, including madder, coffee, tea, etc., according to most authorities.

Cephaelis  (ipecacuanha): Shrub. Tropical and sub-tropical. Bolivia, Colombia. Cultivated in West Indies, Hindustan, India, America.

Cinchona  (Peruvian bark): Trees. Tropical Andes. Cultivated in Ceylon, Jamaica.

Coffea  (coffee): Shrub. Persia. Cultivated in Arabia, East Indies, Mexico, Brazil, Guatemala, Cuba, British West Indies, Santo Domingo, Java, Padang, Sumatra, Macassar, Ceylon, British India, Manila.

Rubia  (madder): Perennial. West Asia, Mediterranean countries.

Order XXXVII.Borraginaceæ: Herbs; sixty-eight genera.

Symphytum  (comfrey): Perennial herb. Peloponnesus and Greek islands. Cultivated in middle Europe and older parts of the United States.

Order XXXVIII.Convolvulaceæ: Herb; thirty-two genera.

Ipomoea  (sweet potato): Perennial. Asia and America. Cultivated in southern United States, Carolinas, Virginia, Maryland, Delaware, southern New Jersey, southern Spain, Italy.

Order XXXIX.Solanaceæ: Herb; sixty-six genera.

Atropa  (deadly nightshade): Europe, western Asia. Cultivated in North America.

Capsicum  (red pepper, cayenne pepper): Annual. South America, southern Asia. Cultivated in southern Europe and in United States, West Indies, middle Africa, southern Asia.

Lycopersicum  (tomato): Annual. South and Central America. Cultivated in Italy, southern France, Spain, Greece, northern Africa, Islands of southern Asia, England (under glass), Virginia, Carolinas.

Nicotiana  (tobacco): Santo Domingo, South Atlantic States of United States of America. Cultivated in Virginia, Kentucky, Carolinas, Venezuela, Cuba, Brazil, Connecticut, Pennsylvania, Holland, Flanders, France, Alsace, Hungary, European Turkey, China, Japan, southern Africa, Australia.

Solanum  (potato): Chile. Cultivated wherever cereals flourish.

Order XL.Pedalineæ: Herb; ten genera.

Sesamum  (sesame): Sunda Islands. Cultivated in India, western Asia, southern Europe, northern Africa, America.

Order XLI.Verbenaceæ: Tree; fifty genera.

Tectona  (teak): Tropical. East Indies, Burma, Philippines.

Order XLII.Labiatæ: Herb; one hundred and thirty-six genera.

Lavandula  (lavender): Greece and Grecian Isles. Cultivated in Hindustan, Atlantic States of North America, Levant.

Marrubium  (hoarhound): Perennial. Levant, Peloponnesus, etc. Cultivated all over Europe, and in Temperate Zone in Asia, and Atlantic States in North America.

Mentha  (pennyroyal): England, Hindustan, Japan, Persia, India, Egypt. In a belt from eastern side of Mississippi Valley to Japan.

Mentha  (spearmint): England, etc., as above.

Nepita  (catnip): Perennial or annual. Europe, western Asia, Levant, North America.

Origanum  (marjoram): Levant, Mediterranean countries, Europe, as far north as fiftieth parallel. Sweet marjoram, native in Greece.

Rosmarius  (rosemary): Evergreen. Southern Europe, Greek islands in the Peloponnesus. Cultivated in western Europe, Japan, Egypt, Hindustan, Asia.

Salvia  (sage): Mediterranean countries. Cultivated in middle-southern Europe, British Isles, North America, British India.

Thymus  (sweet thyme): Perennial. Spain, southern Europe, Mediterranean States, mountains of Greece, and islands of Archipelago, British Isles, southern Siberia.

Order XLIII.Chenopodiaceæ: Herb; eighty genera.

Beta  (beet): Europe and western Asia. Cultivated in Europe, west Africa, temperate British India, North America.

Spinacia  (spinach): Annual. Persia. Cultivated in middle of North Temperate Zone, from Hindustan to western shores and islands of Europe, eastern United States of North America, South Pacific Islands.

Order XLIV.Polygonaceæ: Herb; thirty genera.

Fagopyrum  (buckwheat): Central Asia and Tartary, Russia. Cultivated in Canada, northern United States, northern and central Europe.

Rheum  (rhubarb): Perennial. Tartary. Cultivated as far north as fiftieth parallel, China, especially in provinces of Shensi, Kansu, and Szechuen.

Order XLV.Piperaceæ: Shrub; eight genera.

Piper  (pepper): Southern Asia. Cultivated in southern India, Java, Sumatra, and Malabar.

Order XLVI.Myristicaceæ: Trees, shrubs; one genus.

Myristica  (nutmeg): Molucca Islands. Cultivated in Sumatra, Island of Bourbon, Mauritius, Madagascar, West Indies.

Order XLVII.Lauraceæ: Tree; thirty-four genera.

Cinnamomum  (cinnamon): East India Archipelago. Cultivated in Ceylon, West Indies, South America, Pacific Isles.

Cinnamomum  (camphor): Trees. Japan, Formosa, China, Borneo. The camphor gum of commerce was introduced into Europe by the Arabs.

Order XLVIII.Santalaceæ: Herbs, shrubs, trees; twenty-eight genera.

Santalum  (sandalwood): Trees. East Indies, Asia, Malaysia, Pacific Islands, India, China.

Order XLIX.Euphorbiaceæ: Herbs, shrubs, trees; one hundred and ninety-five genera.

Buxus  (box): Evergreen, shrub, and small trees. Southern Europe, western Asia, Syria, Persia, and south of Black Sea. Cultivated in middle States of North America and Virginia.

Croton  (croton-oil plant): Cultivated in southeastern Hindustan and East India Islands.

Hevea  (caoutchouc): Large tree. South America. Cultivated in southern Asia, middle Africa, northern Australia.

Manihot  (tapioca): Tropical and sub-tropical South America. Cultivated in southern Asia and western Africa.

Ricinus  (castor-oil plant): Annual. Southern Asia, eastern Africa. Cultivated in Japan, Bengal, eastern and northern Africa, southern Europe and United States, especially Kansas.

Order L.Urticaceæ: Trees, shrubs, herbs; one hundred and eight genera.

Cannabis  (hemp): Annual. Chinese Tartary, northern India, southwestern Siberia. Cultivated in China, Japan, Persia, Hindustan, Egypt, southern Africa, Russia, European states, Canada, United States.

Ficus  (fig): Tree. Subtropical. Western Asia. Cultivated through Mediterranean countries west to Canary Isles.

Humulus  (hop): Perennial herb. Middle Europe, Siberia, Levant, Asia Minor, Japan, North America, foot-hills of Rocky Mountains, and along upper Arkansas River, Missouri and Mississippi Rivers, Lake Winnipeg, North Atlantic States. Cultivated in Egypt.

Morus  (mulberry): Tree. Cultivated in western New England, southern upper Canada, Dakotas, Kansas and the South. White mulberry is a native of China and Japan. Cultivated in Italy, Greece, Asia Minor, Armenia.

Ulmus  (elm): Tree. From Mediterranean countries to the middle of European Russia, from southern banks of St. Lawrence River to Gulf of Mexico, and westerly to foot-hills of Rocky Mountains.

Order LI.Juglandaceæ: Trees; five genera.

Juglans  (butternut): Northeastern North Africa. Cultivated in middle Europe and England.

Juglans  (walnut): Southwestern New York and southward to Gulf of Mexico and westward beyond Mississippi River. Cultivated in eastern middle States and southern New England, England and southern Europe.

Hicoria  (hickory nut): North and middle States of North America from Atlantic to Mississippi River, and cultivated in corresponding latitude in Europe.

Hicoria  (pecan nut): Southern North America. Cultivated in Prussia and England.

Order LII.Cupuliferæ: Trees; ten genera.

Castanea  (chestnut): Eastern coast of North America, west to eastern Kentucky and Tennessee. Cultivated in middle and southern England, middle and southern Europe, northern Africa, Levant, and southern and eastern Asia.

Corylus  (hazelnut): Levant. Cultivated between 35° and 55° latitude in Northern Hemisphere, eastern parts of Western Hemisphere, and western Old World.

Fagus  (beech): Temperate Zones up to 60° north latitude, south to 50°.

Quercus  (oak): Temperate Zones above 35°, and in a zone between 30° and 60° around the globe.

Order LIII.Salicaceæ: Shrubs, trees; numerous genera.

Salix  (weeping willow): Western and southern Asia. Cultivated in southern England.

Salix  (curled willow): England. Cultivated in eastern United States.

Angiosperms (Leaves Parallel-Veined)

Order LIV.Orchidaceæ: Woody vine; three hundred and thirty-four genera.

Vanilla  (climbs over lofty trees): Tropical and sub-tropical southern Mexico, coast of Vera Cruz. Cultivated in Guatemala, Mauritius, Bourbon, Madagascar, Java.

Order LV.Zingiberaceæ: Herbs; thirty-six genera.

Curcuma  (turmeric): Farther India and Asiatic isles, southern Asia and Malay Peninsula. Cultivated in Hindustan, Cochin-China, southern India, Bengal, Java, Pacific Isles.

Elettaria  (cardamom): Perennial. Tropical Asia. Cultivated in southern India, Madras, Allepy, Ceylon.

Maranta  (arrowroot): Tropical America, Florida.

Musa  (banana): Asia. Cultivated in Indian Archipelago, China, Cochin-China, Hindustan, Australia, Pacific Islands, Madagascar, western Africa, Sicily, southern Spain, Mexico, Central America, Colombia, Peru, northern Brazil, Guiana, West Indies, southern Florida, and Louisiana.

Musa  (manila): Philippines. Cultivated in India and southern Asia.

Zingiber  (ginger): Sub-tropical. Southern Asia. Cultivated on western coast of Africa, in the West Indies, and southern slopes of Himalayas.

Order LVI.Bromeliaceæ: Herbs; twenty-seven genera.

Ananassa  (pineapple): Perennial root. Tropical. Bahama Islands. Cultivated in South America, Florida, southern shores of Europe, East Africa, Pacific Isles, India.

Order LVII.Iridaceæ: Herbs; fifty-seven genera.

Crocus  (saffron): Throughout southern parts of North Temperate Zone.

Order LVIII.Dioscoreaceæ: Shrubs; eight genera.

Dioscorea  (yam): Tropical and sub-tropical Africa.

Dioscorea  (Chinese yam): America, Asia, Malaysia. Cultivated in Japan, East Indies, Siam.

Order LIX.Liliaceæ: Herbs; one hundred and eighty-seven genera.

Asparagus : Perennial herb. Japan, Levant. Cultivated in England, Holland, central Europe, Mediterranean countries, sandy places of Poland, southern Russia, Hindustan, North America.

Aloe : Southern Asia, Arabia, southern Africa. Cultivated in southern Europe, northern Africa, British West Indies.

Order LX.Palmæ: Shrubs and small and large trees; one hundred and thirty-seven genera.

Areca  (betelnut): Sunda Isles, Philippines, Cochin-China, Sumatra, southern India.

Cocos  (cocoanut): East India Archipelago, Arabia, Persia, Malay. Cultivated in eastern Africa, western America, Brazil, West Indies, islands of Central America.

Metroxylon  (sago palm): Malacca, southern China. Cultivated in Eastern Archipelago.

Phœnix  (date palm): Between 15° and 30° north latitude, from Atlantic Coast to the River Indus; Sahara oases. Cultivated in Acre, Palmyra, Jaffa.

Order LXI.Gramineæ: Herbs; one thousand two hundred and ninety-eight genera.

Avena  (oats): West central Asia, east central Europe. Cultivated in Scotland, Ireland, Norway, Canada, United States.

Hordeum  (barley): Annual. Temperate western Asia. Cultivated in northern Russia, Siberia, etc.

Oryza  (rice): Southern Asia. Cultivated in India, China, Japan, East Indies, Africa, southern Europe, Hungary, South America, southern United States.

Setaria  (millet): China, Japan, India. Cultivated wherever oats and rye are, except in United States.

Saccharum  (sugar-cane): Perennial. Cochin-China. Cultivated in West Indies, Brazil, Mexico, Louisiana, Mississippi, Missouri, Mauritius, southern India, Pacific Islands, northern Australia.

Sorghum  (broom corn): Annual. Middle Africa. Cultivated in southern India, northern Africa, southern and middle Europe, throughout United States.

Secale  (rye): Southern Russia and north of Black and Caspian Seas. Cultivated in northern Germany, Poland, Sweden, Norway, Russia, western Europe, United States.

Triticum  (wheat): Cultivated in western Asia, western America, southern Russia, central and western Europe, southern Italy, Turkey, Syria, northern and southern Africa, Brazil, Chile, Australia. Great wheat-growing regions are southwestern plains of Russia and central plain of North America, and in southern California, northern India, England.

Zea  (Indian corn or maize): America. Cultivated in United States, upper Canada, South America, Mexico, southern Europe, Africa, western Asia.

Order LXII.Coniferæ: Shrubs, trees; thirty-two genera.

Abies  (fir): Northeastern North America, Quebec, New Brunswick, Nova Scotia, middle States, western Wisconsin. Cultivated in England.

Chamæcyparis  (cypress): Evergreen, cypress. Cultivated between 30° and 42° N. latitude in both hemispheres, Carolinas, Georgia, Florida.

Lumpirus  (cedar): Trees and shrubs. Middle and western Europe, northern Asia, North America.

Larix  (larch): Mountains of middle Europe, north of New York to Pacific Ocean.

(2) Gymnosperms (jĭm ´ṉō̇-sperms).—Plants producing naked seeds (i. e., seeds not inclosed in an ovary), as the common pine and hemlock.

This second division of flowering plants (phanerogams ) includes four living groups: (a) Coniferæ, including all evergreen trees, such as pine, fir, redwood (Sequoia ), etc.; (b) Cycadaceæ, trees such as cypress, palmetto, etc.; (c) Gnetaceæ; (d) Ginkgo. There are about five hundred living species.

Order LX.

Order LXX.

Sub-Kingdom II.—Flowerless Plants, or Cryptogamia (krĭp ´ṯō̇-gā´mĭ-ȧ).

(3) Pteridophyta (tĕr-ĭ-dŏf ´ĭ-ta).

This group does not include over five thousand species altogether. All its members have a well-marked differentiation into leaves and stems, some with large leaves like the Bracken fern and some with small leaves like the Club-moss. All are provided with well-differentiated wood and phlœm, which are arranged in bundles in the stem. All the members, also, have a well-marked alternation of generations, but it differs from that of the bryophytes, for the leafy plant which is conspicuous is the spore-producing generation, while the sexual generation is a very small and inconspicuous little structure, as simple as an alga except for its sexual organs. To this cohort belong all the ferns, all the Equisetums, or Horsetails, and the Club-mosses and Selaginellas.

(4) Bryophyta (brĭ-ŏfĭ´-tȧ).

The Bryophyta  form a much smaller group, reported to have about sixteen thousand species. Some of these appear, as do the mosses, to have true leaves, but their apparent leaves are not really like those of the higher plants. They have no true wood or vessels. They have a definite alternation of generations, but the spore-producing generation grows on to the “leafy” sexual generation, and is generally, but wrongly, called its “fruit capsule.” To this group belong the Mosses and Liverworts.

(5) Thallophytes (thāl ´ō-fitz).

The Thallophytes  have the largest number of species after the Angiosperms, and number about eighty thousand species all told. They are all comparatively simple in structure and have no differentiation into stems and roots. The Thallophytes include the algæ, the large fungi, the toadstools, and all the parasitic and disease producing forms of plants.

Algæ are divided into Florideæ, the Red Seaweeds, and the orders DictyoteæOösporeæZoösporeæConjugatæDiatomaceæ, and Cryptophyceæ.

Fungi  include the molds, mildews, mushrooms, puffballs, etc., which are variously grouped into several sub-classes and many orders. The Lichenes  or Lichens are now considered to be of a mixed nature, each plant partly a Fungus and partly an Alga.

The Organic Constituents of Plants

When the water naturally existing in plants is expelled by exposure to the air or a gentle heat, the residual dry matter is found to be composed of a considerable number of different substances, which have been divided into two great classes, called the organic and the inorganic, or mineral constituents of plants. The former are readily combustible, and on the application of heat, catch fire, and are entirely consumed, leaving the inorganic matters in the form of a white residuum or ash. All plants contain both classes of substances; and though their relative proportions vary within very wide limits, the former always greatly exceed the latter, which in many cases form only a very minute proportion of the whole weight of the plant. Owing to the great preponderance of the organic or combustible matters, it was at one time believed that the inorganic substances formed no part of the true structure of plants, and consisted only of a small portion of the mineral matters of the soil, which had been absorbed along with their organic food; but this opinion, which probably was never universally entertained, is now entirely abandoned, and it is no longer doubted that both classes of substances are equally essential to their existence.

Although they form so large a proportion of the plant, its organic constituents are composed of no more than four elements, viz.:—

Carbon.
Hydrogen.
Nitrogen.
Oxygen.

The inorganic constituents are much more numerous, not less than thirteen substances, which appear to be essential, having been observed. These are—

Potash.
Soda.
Lime.
Magnesia.
Peroxide of Iron.
Silicic Acid.
Phosphoric Acid.
Sulphuric Acid.
Chlorine.

And more rarely

Manganese.
Iodine.
Bromine.
Fluorine.

Several other substances, among which may be mentioned alumina and copper, have also been enumerated; but there is every reason to believe that they are not essential, and the cases in which they have been found are quite exceptional.

It is to be especially noticed that none of these substances occur in plants in the free or uncombined state, but always in the form of compounds of greater or less complexity, and extremely varied both in their properties and composition.

It would be out of place, in a work like the present, to enter into complete details of the properties of the elements of which plants are composed, which belongs strictly to pure chemistry, but it is necessary to premise a few observations regarding the organic elements, and their more important compounds.

Carbon.—When a piece of wood is heated in a close vessel, it is charred, and converted into charcoal. This charcoal is the most familiar form of carbon, but it is not absolutely pure, as it necessarily contains the ash of the wood from which it was made. In its purest form it occurs in the diamond, which is believed to be produced by the decomposition of vegetable matters, and it is there crystallized and remarkably transparent; but when produced by artificial processes, carbon is always black, more or less porous, and soils the fingers. It is insoluble in water, burns readily, and is converted into carbonic acid. Carbon is the largest constituent of plants, and forms, in round numbers, about 50 per cent of their weight when dry.

Carbonic Acid.—This, the most important compound of carbon and oxygen, is best obtained by pouring a strong acid upon chalk or limestone, when it escapes with effervescence. It is a colourless gas, extinguishing flame, incapable of supporting respiration, much heavier than atmospheric air, and slightly soluble in water, which takes up its own volume of the gas. It is produced abundantly when vegetable matters are burnt, as also during respiration, fermentation, and many other processes. It is likewise formed daring the decay of animal and vegetable matters, and is consequently evolved from dung and compost heaps.

Hydrogen  occurs in nature only in combination. Its principal compound is water, from which it is separated by the simultaneous action of an acid, such as sulphuric acid and a metal, in the form of a transparent gas, lighter than any other substance. It is very combustible, burns with a pale blue flame, and is converted into water. It is found in all plants, although in comparatively small quantity, for, when dry, they rarely contain more than four or five per cent. Its most important compound is water, of which it forms one-ninth, the other eight-ninths consisting of oxygen.

Nitrogen  exists abundantly in the atmosphere, of which it forms nearly four-fifths, or, more exactly, 79 per cent. It is there mixed, but not combined with oxygen; and when the latter gas is removed, by introducing into a bottle of air some substance for which the former has an affinity, the nitrogen is left in a state of purity. It is a transparent gas, which is incombustible and extinguishes flame. It is a singularly inert substance, and is incapable of directly entering into union with any other element except oxygen, and with that it combines with the greatest difficulty, and only by the action of the electric spark—a peculiarity which has very important bearings on many points we shall afterwards have to discuss. Nitrogen is found in plants to the extent of from 1 to 4 per cent.

Nitric Acid.—This, the most important compound of nitrogen and oxygen, can be produced by sending a current of electric sparks through a mixture of its constituents, but in this way it can be obtained only in extremely small quantity. It is much more abundantly produced when organic matters are decomposed with free access of air, in which case the greater proportion of their nitrogen combines with the atmospheric oxygen. This process, which is known by the name of nitrification, is greatly promoted by the presence of lime or some other substance, with which the nitric acid may combine in proportion as it is formed. It takes place, to a great extent, in the soil in India and other hot climates; and our chief supplies of saltpetre, or nitrate of potash, are derived from the soil in these countries, where it has been formed in this manner. The same change occurs, though to a much smaller extent, in the soil in temperate climates.

Ammonia  is a compound of nitrogen and hydrogen, but it cannot be formed by the direct union of these gases. It is a product of the decomposition of organic substances containing nitrogen, and is produced when they are distilled at a high temperature, or allowed to putrefy out of contact of the air. In its pure state it is a transparent and colourless gas, having a peculiar pungent smell, and highly soluble in water. It is an alkali resembling potash and soda, and, like these substances, unites with the acids and forms salts, of which the sulphate and muriate are the most familiar. In these salts it is fixed, and does not escape from them unless they be mixed with lime, or some other substance possessing a more powerful affinity for the acid with which it is united.

Oxygen  is one of the most widely distributed of all the elements, and, owing to its powerful affinities, is the most important agent in almost all natural changes. It is found in the air, of which it forms 21 per cent, and in combination with hydrogen, and almost all the other chemical elements. In the pure state it possesses very remarkable properties. All substances burn in it with greater brilliancy than they do in atmospheric air, and its affinity for most of the elements is extremely powerful. When diluted with nitrogen, it supports the respiration of animals; but in the pure state it proves fatal after the lapse of an hour or two. It is found in plants, in quantities varying from 30 to 36 per cent.

It is worthy of observation, that of the four organic elements, carbon only is fixed, and the other three are gases; and likewise, when any two of them unite, their compound is either a gaseous or a volatile substance. The charring of organic substances, which is one of their most characteristic properties, and constantly made use of by chemists as a distinctive reaction, is due to this peculiarity; for when they are heated, a simpler arrangement of their particles takes place, the hydrogen, nitrogen, and oxygen unite among themselves, and carry off a small quantity of carbon, while the remainder is left behind in the form of charcoal, and is only consumed when access of the external air is permitted.

Now, in order that a plant may grow, its four organic constituents must be absorbed by it, and that this absorption may take place, it is essential that they be presented to it in suitable forms. A seed may be planted in pure carbon, and supplied with unlimited quantities of hydrogen, nitrogen, oxygen, and inorganic substances, and it will not germinate; and a plant, when placed in similar circumstances, shows no disposition to increase, but rapidly languishes and dies. The obvious inference from these facts is, that these substances cannot be absorbed when in the elementary  state, but that it is only after they have entered into certain forms of combination that they acquire the property of being readily taken up, and assimilated by the organs of the plant.

It was at one time believed that many different compounds of these elements might be absorbed and elaborated, but later and more accurate experiments have reduced the number to four—namely, carbonic acid, water, ammonia, and nitric acid. The first supplies carbon, the second hydrogen, the two last nitrogen, while all of them, with the exception of ammonia, may supply the plant with oxygen as well as with that element of which it is the particular source.

There are only two sources from which these substances can be obtained by the plant, viz. the atmosphere and the soil, and it is necessary that we should here consider the mode in which they may be obtained from each.

The Atmosphere as a source of the Organic Constituents of Plants.—Atmospheric air consists of a mixture of nitrogen and oxygen gases, watery vapour, carbonic acid, ammonia, and nitric acid. The two first are the largest constituents, and the others, though equally essential, are present in small, and some of them in extremely minute quantity. When deprived of moisture and its minor constituents, 100 volumes of air are found to contain 21 of oxygen and 79 of nitrogen. Although these gases are not chemically combined in the air, but only mechanically mixed, their proportion is exceedingly uniform, for analyses completely corresponding with these numbers have been made by Humboldt, Gay-Lussac, and Dumas at Paris, by Saussure at Geneva, and by Lewy at Copenhagen; and similar results have also been obtained from air collected by Gay-Lussac during his ascent in a balloon at the height of 21,430 feet, and by Humboldt on the mountain of Antisano in South America at a height of 16,640 feet. In short, under all circumstances, and in all places, the relation subsisting between the oxygen and nitrogen is constant; and though, no doubt, many local circumstances exist which may tend to modify their proportions, these are so slow and partial in their operations, and so counterbalanced by others acting in an opposite direction, as to retain a uniform proportion between the main constituents of the atmosphere, and to prevent the undue accumulation of one or other of them at any one point.

No such uniformity exists in the proportion of the minor constituents. The variation in the quantity of watery vapour is a familiar fact, the difference between a dry and moist atmosphere being known to the most careless observer, and the proportions of the other constituents are also liable to considerable variations.

Carbonic Acid.—The proportion of carbonic acid in the air has been investigated by Saussure. From his experiments, made at the village of Chambeisy, near Geneva, it appears that the quantity is not constant, but varies from 3·15 to 5·75 volumes in 10,000; the mean being 4·15. These variations are dependent on different circumstances. It was found that the carbonic acid was always more abundant during the night than during the day—the mean quantity in the former case being 4·32, in the latter 3·38. The largest quantity found during the night was 5·74, during the day 5·4. Heavy and continued rain diminishes the quantity of carbonic acid, by dissolving and carrying it down into the soil. Saussure found that in the month of July 1827, during the time when nine millimetres of rain fell, the average quantity of carbonic acid amounted to 5·18 volumes in 10,000; while in September 1829, when 254 millimetres fell, it was only 3·57. A moist state of the soil, which is favourable to the absorption of carbonic acid, also diminishes the quantity contained in the air, while, on the other hand, continued frosts, by retaining the atmosphere and soil in a dry state, have an opposite effect. High winds increase the carbonic acid to a small extent. It was also found to be greater over the cultivated lands than over the lake of Geneva; at the tops of mountains than at the level of the sea; in towns than in the country. The differences observed in all these cases, though small, are quite distinct, and have been confirmed by subsequent experimenters.

Ammonia.—The presence of ammonia in the atmosphere appears to have been first observed by Saussure, who found that when the sulphate of alumina is exposed to the air, it is gradually converted into the double sulphate of alumina and ammonia. Liebig more recently showed that ammonia can always be detected in rain and snow water, and it could not be doubted that it had been absorbed from the atmosphere. Experiments have since been made by different observers with the view of determining the quantity of atmospheric ammonia, and their results are contained in the subjoined table, which gives the quantity found in a million parts of air.

Kemp 3·6800
Pierre {12 feet above the surface 3·5000
{25 feet do.        do.0·5000
Graeger 0·3230
Fresenius {By day 0·0980
{By night 0·1690
Ville {{Maximum 0·0317
{ In Paris {Minimum 0·0177
{{Mean 0·0237
{{Maximum 0·0276
{ Environs {Minimum 0·0165
{ of Paris {Mean 0·0210

Of these results, the earlier ones of Kemp, Pierre, and Graeger are undoubtedly erroneous, as they were made without those precautions which subsequent experience has shown to be necessary. Even those of the other observers must be taken as giving only a very general idea of the quantity of ammonia in the air, for a proportion so minute as one fifty-millionth cannot be accurately determined even by the most delicate experiments. For this reason, more recent experimenters have endeavoured to arrive at conclusions bearing more immediately upon agricultural questions, by determining the quantity of ammonia brought down by the rain. The first observations on this subject were made by Barral in 1851, and they have been repeated during the years 1855 and 1856 by Mr. Way. In 1853, Boussingault also made numerous experiments on the quantity of ammonia in the rain falling at different places, as well as in dew and the moisture of fogs. He found in the imperial gallon—

Grs.
Rain { Paris 0·2100
{ Liebfrauenberg 0·0350
Dew,Liebfrauenberg { Maximum 0·4340
{ Minimum 0·0714
{ Liebfrauenberg 0·1790
Fog { Paris 9·6000

It thus appears that in Paris the quantity of ammonia in rain-water is just six times as great as it is in the country, a result, no doubt, due to the ammonia evolved during the combustion of fuel, and to animal exhalations, and to the same cause, the large quantity contained in the moisture of fogs in Paris may also be attributed. Barral and Way have made determinations of the quantity of ammonia carried down by the rain in each month of the year, the former using for this purpose the water collected in the rain-gauges of the Paris Observatory, and representing, therefore, a town atmosphere; the latter, that from a large rain-gauge at Rothamsted, at a distance from any town. According to Barral the ammonia annually deposited on an acre of land amounts to 12·28 lbs., a quantity considerably exceeding that obtained by Way, whose experiments being made at a distance from towns, must be considered as representing more accurately the normal condition of the air. His results for the years 1855 and 1856 are given below, along with the quantities of nitric acid found at the same time.

Nitric Acid.—The presence of nitric acid in the air appears to have been first observed by Priestley at the end of the last century, but Liebig, in 1825, showed that it was always to be found after thunder-storms, although he failed to detect it at other times. In 1851 Barral proved that it is invariably present in rain-water, and stated the quantity annually carried down to an acre of land at no less than 41·29 lbs. But at the time his experiments were made, the methods of determining very minute quantities of nitric acid were exceedingly defective, and Way, by the adoption of an improved process, has shown that the quantity is very much smaller than Barral supposed, and really falls short of three pounds. His results for ammonia, as well as nitric acid, are given in the subjoined table.

 Nitric Acid in Grains.Ammonia in Grains.Total Nitrogen in Grains.
 1855.1856.1855.1856.1855.1856.
January 230 1564 1244 5,005 1084 4,526
February 944 544 2337 4,175 2169 3,579
March 1102 866 4513 2,108 3995 1,945
April 325 1063 1141 8,614 1024 7,369
May 1840 3024 4206 18,313 3939 15,863
June 3303 2046 5574 4,870 5447 4,540
July 2680 1191 9620 2,869 8615 2,670
August 3577 2125 4769 4,214 4870 4,021
September 732 1756 3313 5,972 2917 5,373
October 4480 2075 7592 3,921 7414 3,767
November 1007 1371 3021 2,591 2749 2,489
December 664 2035 2438 4,070 2180 3,352
Total in pounds for the whole year 2·98 ·280 7·11 9·53 6·63 8·31

No attempts have been made to determine the proportion of nitric acid in air, but its quantity is undoubtedly excessively minute, and materially smaller than that of ammonia. At least this conclusion seems to be a fair inference from Way's researches, as well as the recent experiments of Boussingault on the proportion of nitric acid contained in rain, dew, and fog, made in a manner exactly similar to those on the ammonia, already quoted. According to his experiments an imperial gallon contains—

Grs.
Rain.{Paris 0·0708
{Liebfrauenberg 0·0140
Dew.{Maximum 0·0785
{Minimum 0·0030
Fog.{Paris 0·7092
{Liebfrauenberg 0·0718

Although it thus appears that Barral's results have been only partially confirmed, enough has been ascertained to show that the quantity of ammonia and nitric acid in the air is sufficient to produce a material influence in the growth of plants. The large amount of these substances contained in the dew is also particularly worthy of notice, and may serve to some extent to explain its remarkably invigorating effect on vegetation.

Carburetted Hydrogen.—Gay-Lussac, Humboldt, and Boussingault have shown, that when the whole of the moisture and carbonic acid have been removed from the air, it still contains a small quantity of carbon and hydrogen; and Saussure has rendered it probable that they exist in a state of combination as carburetted hydrogen gas. No definite proof of this position has, however, as yet been adduced, and the function of the compound is entirely unknown. It is possible that the presence of carbon and hydrogen may be due to a small quantity of organic matter; but, whatever be its source, its amount is certainly extremely small.

Sulphuretted Hydrogen and Phosphuretted Hydrogen.—The proportion of these substances is almost infinitesimal; but they are pretty general constituents of the atmosphere, and are apparently derived from the decomposition of animal and vegetable matters.

The preceding statements lead to the important conclusion, that the atmosphere is capable of affording an abundant supply of all the organic elements of plants, because it not only contains nitrogen and oxygen in the free state, but also in those forms of combination in which they are most readily absorbed, as well as a large quantity of carbonic acid, from which their carbon may be derived. At first sight it may indeed appear that the quantity of the latter compound, and still more that of ammonia, is so trifling as to be of little practical importance. But a very simple calculation serves to show that, though relatively small, they are absolutely large, for the carbonic acid contained in the whole atmosphere amounts in round numbers to

2,400,000,000,000 tons,

and the ammonia, assuming it not to exceed one part in fifty millions, must weigh

74,000,000 tons,

quantities amply sufficient to afford an abundant supply of these elements to the whole vegetation of our globe.

The Soil as a Source of the Organic Constituents of Plants.—When a portion of soil is subjected to heat, it is found that it, like the plant, consists of a combustible and an incombustible part; but while in the plant the incombustible part or ash is small, and the combustible large, these proportions are reversed in the soil, which consists chiefly of inorganic or mineral matters, mixed with a quantity of combustible or organic substances, rarely exceeding 8 or 10 per cent, and often falling considerably short of this quantity.

The organic matter exists in the form of a substance called humus, which must be considered here as a source of the organic constituents of plants, independently of the general composition of the soil, which will be afterwards discussed.

The term humus  is generic, and applied by chemists to a rather numerous group of substances, very closely allied in their properties, several of which are generally present in all fertile soils. They have been submitted to examination by various chemists, but by none more accurately than by Mulder and Herman, to whom, indeed, we owe almost all the precise information we possess on the subject. The organic matters of the soil may be divided into three great classes; the first containing those substances which are soluble in water; the second, those extracted by means of caustic potash; and the third, those insoluble in all menstrua. When a soil is boiled with a solution of caustic potash, a deep brown fluid is obtained, from which acids precipitate a dark brown flocculent substance, consisting of a mixture of at least three different acids, to which the names of humic, ulmic, and geic acids have been applied. The fluid from which they have been precipitated contains two substances, crenic and apocrenic acids, while the soil still retains what has been called insoluble humus.

The acids above named do not differ greatly in chemical characters, but they have been subdivided into the humic, geic, and crenic groups, which present some differences in properties and composition. They are compounds of carbon, hydrogen, and oxygen, and are characterised by so powerful an affinity for ammonia that they are with difficulty obtained free from that substance, and generally exist in the soil in combination with it. They are all products of the decomposition of vegetable matters in the soil, and are formed during their decay by a succession of changes, which may be easily traced by observing the course of events when a piece of wood or any other vegetable substance is exposed for a length of time to air and moisture. It is then found gradually to disintegrate with the evolution of carbonic acid, acquiring first a brown and finally a black colour. At one particular stage of the process it is converted into one or other of two substances, called humin and ulmin, both insoluble in alkalies, and apparently identical with the insoluble humus of the soil; but when the decomposition is more advanced the products become soluble in alkalies, and then contain humic, ulmic, and geic acids, and finally, by a still further progress, crenic and apocrenic acids are formed as the result of an oxidation occurring at certain periods of the decay.

The roots and other vegetable debris remaining in the soil undergo a similar series of changes, and form the humus, which is found only in the surface soil, that is to say, in the portion which is now or has at some previous period been occupied by plants, and the quantity of humus contained in any soil is mainly dependent on the activity of vegetation on it. Numerous analyses of humus compounds extracted from the soil have been made, and have served to establish a number of minor differences in the composition even of those to which the same name has been applied, due manifestly to the fact that their production is the result of a gradual decomposition, which renders it impossible to extract from the soil one pure substance, but only a variable mixture of several, so similar to one another in properties, that their separation is very difficult, if not impossible. For this reason great discrepancies exist in the statements made regarding them by different observers, but this is a matter of comparatively small importance, as their exact composition has no very direct bearing on agricultural questions, and it will suffice to give the names and chemical formulæ of those which have been analysed and described,—

Ulmic acid from long Frisian turf C 40 H 18 O 16
Humic acid from hard turf C 40 H 15 O 15
Humic acid from arable soil C 40 H 16 O 16
Humic acid from a pasture field C 40 H 14 O 14
Geic acid C 40 H 15 O 17
Apocrenic acid C 48 H 12 O 24
Crenic acid C 24 H 12 O 16

It is only necessary to observe further, that these formulæ indicate a close connection with woody fibre, and the continuous diminution of the hydrogen and increase of oxygen shows that they must have been produced by a gradually advancing decay.

The earlier chemists and vegetable physiologists attributed to the humus of the soil a much more important function than it is now believed to possess.

It was formerly considered to be the exclusive, or at least the chief source of the organic constituents of plants, and by absorption through the roots to yield to them the greater part of their nutriment. But though this view has still some supporters, among whom Mulder is the most distinguished, it is now generally admitted that humus is not a direct  source of the organic constituents of plants, and is not absorbed as such by their roots, although it is so indirectly, in as far as the decomposition which it is constantly undergoing in the soil yields carbonic acid, which can be absorbed. The older opinion is refuted by many well-ascertained facts. As regards the exclusive origin of the carbon of plants from humus, it is easy to see that this at least cannot be true, for humus, as already stated, is itself derived solely from the decomposition of vegetable and animal matters; and if the plants on the earth's surface were to be supported by it alone, the whole of their substance would have to return to the soil in the same form, in order to supply the generation which succeeds them. But this is very far from being the case, for the respiration of animals, the combustion of fuel, and many other processes, are annually converting a large quantity of these matters into carbonic acid; and if there were no other source of carbon but the humus of the soil, the amount of vegetable life would gradually diminish, and at length become entirely extinct. Schleiden, who has discussed this subject very fully, has made an approximative calculation of the total quantity of humus on the earth's surface, and of the carbon annually converted into carbonic acid by the respiration of man and animals, the combustion of wood for fuel, and other minor processes; and he draws the conclusion that, if there were no other source of carbon except humus, the quantity of that substance existing in the soil would only support vegetation for a period of sixty years.

The particular phenomena of vegetation also afford abundant evidence that humus cannot be the only source of carbon. Thus Boussingault has shown that on the average of years, the crops cultivated on an acre of land remove from it about one ton more organic matter than they receive in the manure applied to them, although there is no corresponding diminution in the quantity of humus contained in the soil. An instance which leads still more unequivocally to the same conclusion is given by Humboldt. He states that an acre of land, planted with bananas, yields annually about 152,000 pounds weight of fruit, containing about 32,000 pounds, or almost exactly 14 tons of carbon; and as this production goes on during a period of twenty years, there must be withdrawn in that time no less than 280 tons of carbon. But the soil on an acre of land weighs, in round numbers, 1000 tons, and supposing it to contain 4 per cent of humus, the total weight of carbon in it would amount to little more than 20 tons.

It is obvious from these and many other analogous facts that humus cannot be the only or even a considerable source of the carbon of plants, although it is still contended by some chemists that it may be absorbed to a small extent. But even this is at variance with many well-known facts. For if humus were absorbed, it might be expected that vegetation would be most luxuriant on soils containing abundance of that substance, especially if it existed in a soluble and readily absorbable form; but so far from this being the case, nothing is more certain than that peat, in which these conditions are fulfilled, is positively injurious to most plants. On the other hand, our daily experience affords innumerable examples of plants growing luxuriantly in soils and places where no humus exists. The sands of the sea-shore, and the most barren rocks, have their vegetation, and the red-hot ashes which are thrown out by active volcanoes are no sooner cool than a crop of plants springs up on them.

The conclusions to be drawn from these considerations have been further confirmed by the direct experiments of different observers. Boussingault sowed peas, weighing 15·60 grains, in a soil composed of a mixture of sand and clay, which had been heated red-hot, and consequently contained no humus, and after 99 days' growth, during which they had been watered with distilled water, he found the crop to weigh 68·72 grains, so that there had been a fourfold increase. Similar experiments have been made by Prince Salm Horstmar, on oats and rape sown in a soil deprived of organic matter by ignition, in which they grew readily, and arrived at complete maturity. One oat straw attained a height of three feet, and bore 78 grains; another bore 47; and a third 28—in all 153. These when dried at 212° weighed 46·302 grains, and the straw 45·6 grains. The most satisfactory experiments, however, are those of Weigman and Polstorf, these observers having found that it was possible to obtain a two-hundred-fold produce of barley in an entirely artificial soil, provided care was taken to give it the physical  characters of a fertile soil. They prepared a mixture of six parts of sand, two of chalk, one of white bole, and one of wood charcoal; to which was added a small quantity of felspar, previously fused with marble and some soluble salts, so as to imitate as closely as possible the inorganic parts of a soil, and in it they planted twelve barley pickles. The plants grew luxuriantly, reaching a height of three feet, and each bearing nine ears, containing 22 pickles. The grain of the twelve plants weighed 2040 grains.

These experiments show that plants can grow and produce seed when the most scrupulous care is taken to deprive them of every trace of humus. But Saussure has gone further, and shown that even when present, humus is not absorbed. He allowed plants of the common bean and the Polygonum Persicaria to grow in solutions of humate of potash, and found a very trifling diminution in the quantity of humic acid present; but the value of his experiments is invalidated by his having omitted to ascertain whether the diminution of humic acid which he observed was really due to absorption by the plant. This omission has been supplied by Weigman and Polstorf. They grew plants of mint (Mentha undulata) and of Polygonum Persicaria in solutions of humate of potash, and placed beside the glass containing the plant, another perfectly similar, and containing only the solution of humate of potash. The solution, which contained in every 100 grains, 0·148 grains of solid matter, consisting of humate of potash, etc. was found to become gradually paler, and at the end of a month, during which time the plants had increased by 6-1/2 inches, the quantity of solid matter in 100 grains had diminished to 0·132. But the solution contained in the other glass, and in which no plant had grown, had diminished to 0·136, so that the absorption could not have amounted to more than 0·004 grains for every 100 grains of solution employed. This quantity is so small as to be within the limits of error of experiment, and we are consequently entitled to draw the conclusion that humus, even under the most favourable circumstances, is not absorbed by plants.

But though not directly capable of affording nutriment to plants, it must not, on that account, be supposed that humus is altogether devoid of importance, for it is constantly undergoing decomposition in the soil, and thus becomes a source of carbonic acid which can be absorbed, and, as we shall afterwards more particularly see, it exercises very important functions in bringing the other constituents of the soil into readily available forms of combination.

It has been already observed that carbon, hydrogen, nitrogen, and oxygen, cannot be absorbed by plants when uncombined, but only in the forms of water, carbonic acid, ammonia, and nitric acid. It is scarcely necessary to detail the grounds on which this conclusion has been arrived at in regard to carbon and hydrogen, for practically it is of little importance whether they can be absorbed or not, as the former is rarely, the latter never, found uncombined in nature. Neither can there be any doubt that water and carbonic acid are the only substances from which these elements can be obtained. Every-day experience convinces us that water is essential to vegetation; and Saussure, and other observers, have shown that plants will not grow if they are deprived of carbonic acid, and that they actually absorb that substance abundantly from the atmosphere. The evidence for the non-absorption of oxygen lies chiefly in the fact that plants obtain, in the form of water and carbonic acid, a larger quantity of that element than they require, and in place of absorbing, are constantly exhaling it. The form in which nitrogen may be absorbed has given rise to much difference of opinion. In the year 1779, Priestley commenced the examination of this subject, and drew from his experiments the conclusion, that plants absorb the nitrogen of the air. Saussure shortly afterwards examined the same subject, and having found, that when grown in a confined space of air, and watered with pure water, the nitrogen of the plants underwent no increase, he inferred that they derived their entire supplies of that element from ammonia, or the soluble nitrogenous constituents of the soil or manure. Boussingault has since re-examined this question, and by a most elaborate series of experiments, in which the utmost care was taken to avoid every source of fallacy, he was led to the conclusion, that when haricots, oats, lupins, and cresses were grown in calcined pumice-stone, mixed with the ash of plants, and supplied with air deprived of ammonia and nitric acid, their nitrogen underwent no increase. It has been objected to these experiments, that the plants being confined in a limited bulk of air, were placed in an unnatural condition, and Ville has recently repeated them with a current of air passing through the apparatus, and found a slight increase in the nitrogen, due, as he thinks, to direct absorption. It is much more probable, however, that it depends on small quantities of ammonia or nitric acid which had not been completely removed from the air by the means employed for that purpose, for nothing is more difficult than the complete abstraction of these substances, and as the gain of nitrogen was only 0·8 grains, while 60,000 gallons of air, and 13 of water, were employed in the experiment, which lasted for a considerable time, it is reasonable to suppose that a sufficient quantity may have remained to produce this trifling increase.

While these experiments show that plants maintain only a languid existence when grown in air deprived of ammonia and nitric acid, and hence, that the direct absorption of nitrogen, if it occur at all, must do so to a very small extent, the addition of a very minute quantity of the former substance immediately produces an active vegetation and rapid increase in size of the plants. Among the most striking proofs of this are the experiments of Wolff, made by growing barley and vetches in a soil calcined so as to destroy organic matters, and then mixed with small quantities of different compounds of ammonia. He found that when the produce from the calcined soil was represented by 100, that from the different ammoniacal salts was—

Barley.Vetches.
Muriate of Ammonia 257·2 176·4
Carbonate of Ammonia 123·6 173·8
Sulphate of Ammonia 203·6 125·2

These experiments not only prove that ammonia can be absorbed, but they also indirectly confirm the statement already made, that humus is not necessary; for in some instances the produce was higher than that obtained from the uncalcined soil with the same manures, although it contained four per cent of humus.

On such experiments Liebig rests his opinion that ammonia is the exclusive source of the nitrogen of plants, and although he has recently admitted that it may be replaced by nitric acid, it is obvious that he considers this a rare and exceptional occurrence. The evidence, however, for the absorption of nitric acid appears to rest on as good grounds as that of ammonia, for experience has shown that nitrate of soda acts powerfully as a manure, and its effect must be due to the nitric acid, and not to the soda, for the other compounds of that alkali have no such effect. Wolff has illustrated this point by a series of experiments on the sunflower, of which we shall quote one. He took two seeds of that plant, and sowed them on the 10th May, in a soil composed of calcined sand, mixed with a small quantity of the ash of plants, and added at intervals during the progress of the experiment, a quantity of nitrate of potash, amounting in all to 17·13 grains. The plants were watered with distilled water, containing carbonic acid in solution, and the pot in which they grew was protected from rain and dew by a glass cover. On the 19th August one of the plants had attained a height of above 28 inches, and had nine fine leaves and a flower-bud; the other was about 20 inches high, and had ten leaves. On the 22d August, one of the plants having been accidentally injured, the experiment was terminated. The plants, which contained 103·16 grains of dry matter, were then carefully analysed, and the quantity of nitrogen contained in the soil after the experiment and in the seed was determined.

Grains.
Nitrogen in the dry plants 1·737 }
"remaining in the soil 0·697 }2·434
"in the nitrate of potash 2·370 }
"in the seeds 0·029 }2·399
———
Difference 0·035

Hence, the nitrogen contained in the plants must, in this instance, have been obtained entirely from the nitrate of potash, for the quantity contained in it and in the seeds is exactly equal to that in the plants and the soil, the difference of 0·03 grains being so small that it may be safely attributed to the errors inseparable from such experiments. For the sake of comparison, an exactly similar experiment was made on two seeds grown without nitrate of potash, and in this instance, after an equally long period of growth, the largest plant had only attained a height of 7·5 inches, and had three small pale and imperfectly developed leaves. They contained only 0·033 grains of nitrogen, while the seeds contained 0·032—indicating that, under these circumstances, there was no increase in the quantity of that element.

But, independently of these experimental results, it may be inferred from general considerations, that nitric acid must be one of the sources from which plants derive their nitrogen. It has been already stated, that the humus contained in the soil consists of the remains of decayed plants, and there is every reason to suppose that the primeval soil contained no organic matters, and that the first generation of plants must have derived the whole of their nitrogen from, the atmosphere. If, therefore, it be assumed that ammonia is the only source of the nitrogen of plants, it would follow, that as that substance cannot be produced by the direct union of its elements, the quantity of ammonia in the air could only remain undiminished in the event of the whole of the nitrogen of decaying plants returning into that form. But this is certainly not the case, for every time a vegetable substance is burned, part of its nitrogen is liberated in the free state, and in certain conditions of putrefaction, nitric acid is produced. Now, if ammonia be the only form in which nitrogen is absorbed, there must be a gradual diminution of the quantity contained in the air; and further, there must either be some continuous source of supply by which its quantity is maintained, or there must be some other substance capable of affording nitrogen in a form fitted for the maintenance of plant life. As regards the first alternative, it must be stated that we know of no source other than the decomposition of plants from which ammonia can be derived, and we are therefore compelled to adopt the second alternative, and to admit that there must be some other source of nitrogen, and it cannot be doubted, from what has been already stated, that it is from nitric acid only that it can be obtained.

It must be admitted, then, that carbonic acid, ammonia, nitric acid, and water, are the great organic foods of plants. But while they have afforded to them an inexhaustible supply of the last, the quantity of the other three available for food are limited, and insufficient to sustain their life for a prolonged period. It has been shown by Chevandrier, that an acre of land under beech wood accumulates annually about 1650 lb. of carbon. Now, the column of air resting upon an acre of land contains only about 15,500 lb. of carbon, and the soil may be estimated to contain 1 per cent., or 22,400 lb. per acre, and the whole of this carbon would therefore be removed, both from the air and the soil, in the course of little more than 23 years. But it is a familiar fact, that plants continue to grow with undiminished luxuriance year after year in the same soil, and they do so because neither their carbon nor their nitrogen are permanently absorbed; they are there only for a period, and when the plant has finished its functions, and dies, they sooner or later return into their original state. Either the plant decays, in which case its carbon and nitrogen pass more or less rapidly into their original state, or it becomes the food of animals, and by the processes of respiration and secretion, the same change is indirectly effected. In this way a sort of balance is sustained; the carbon, which at one moment is absorbed by the plant, passes in the next into the tissues of the animal, only to be again expired in that state in which it is fitted to commence again its round of changes.

But while there is thus a continuous circulation of these constituents through both plants and animals, there are various changes which tend to liberate in the free state a certain quantity both of the carbon and nitrogen of plants, and these being thus removed from the sphere of organic life, there would be a gradual diminution in the amount of vegetation at the earth's surface, unless this loss were counterbalanced by some corresponding source of gain. In regard to carbonic acid the most important source is volcanic action, but the loss of nitrogen, which is far more important and considerable, is restored by the direct combination of its elements. The formation of nitric acid during thunder storms has been long familiar; but it would appear from the recent experiments of Clöez, which, should they be confirmed by farther enquiry, will be of much importance, that this compound is also produced without electrical action when air is passed over certain porous substances, saturated with alkaline and earthy compounds. Fragments of calcined brick and pumice stone were saturated with solution of carbonate of potash, with carbonates of lime and magnesia and other mixtures, and a current of air freed from nitric acid and ammonia passed over them for a long period, at the end of which notable quantities of nitric acid were detected.

Source of the Inorganic Constituents of Plants.—The inorganic constituents of plants being all fixed substances, it is sufficiently obvious that they can only be obtained from the soil, which, as we shall afterwards see, contains all of them in greater or less abundance, and has always been admitted to be the only substance capable of supplying them. The older chemists and physiologists, however, attributed no importance to these substances, and from the small quantities in which they are found in plants, imagined that they were there merely accidental impurities absorbed from the soil along with the humus, which was at that time considered to be their organic food. This opinion, sufficiently disproved by the constant occurrence of the same substances in nearly the same proportions, in the ash of each individual plant, has been further refuted by the experiments of Prince Salm Horstmar, who has established their importance to vegetation, by experiments upon oats grown on artificial soils, in each of which one inorganic constituent was omitted. He found that, without silica, the grain vegetated, but remained small, pale in colour, and so weak as to be incapable of supporting itself; without lime, it died when it had produced its second leaf; without potash and soda, it grew only to the height of three inches; without magnesia, it was weak and incapable of supporting itself; without phosphoric acid, weak but upright; and without sulphuric acid, though normal in form, the plant was feeble, and produced no fruit.

Manner in which the Constituents of Plants are absorbed.—Having treated of the sources of the elements of plants, it is necessary to direct attention to the mode in which they enter their system.

Water.—The absorption of water by plants takes place in great abundance, and is connected with many of the most important phenomena of vegetation. It is principally absorbed by the roots, and passes into the tissues of the plant, where a part of it is decomposed, and goes to the formation of certain of its organic compounds; while by far the larger quantity, in place of remaining in it, is again exhaled by the leaves. The extent to which this takes place is very large. Hales found that a sunflower exhaled in twelve hours about 1 lb. 5 oz. of water, but this quantity was liable to considerable variation, being greater in dry, and less in wet weather, and much diminished during the night. Saussure made similar experiments, and observed that the quantity of water exhaled by a sunflower amounted to about 220 lb. in four months. The exhalation of plants has recently been examined with great accuracy by Lawes. His experiments were made by planting single plants of wheat, barley, beans, peas, and clover, in large glass jars capable of holding about 42 lb. of soil, and covered with glass plates, furnished with a hole in the centre for the passage of the stem of the plant. Water was supplied to the soil at certain intervals, and the jars were carefully weighed. The result of the experiments, continued during a period of 172 days, is given in the following table, which shows the total quantity of water exhaled in grains:—

Wheat 113,527
Barley 120,025
Beans 112,231
Peas 109,082
Clover, cut 28th June 55,093

It further appears, that the exhalation is not uniform, but increases during the active growth of the plant, and diminishes again when that period is passed. These variations are shown by the subjoined tables, of which the first gives the total exhalation, and the second the average daily loss of water during certain periods.

Table I.—Showing the Number of Grains of Water given off by the Plants during stated divisional Periods of their Growth

Description of Plant.9 Days.31 Days.27 Days.34 Days.30 Days.14 Days.27 Days.
From Mar. 19 to Mar. 28.From Mar. 28 to Apr. 28.From Apr. 28 to May 25.From May 25 to June 28.From June 28 to July 28.From July 28 to Aug. 11.From Aug. 11 to Sept. 7.
Wheat 129 1268 4,385 40,030 46,060 15,420 6235
Barley 129 1867 12,029 37,480 45,060 17,046 6414
Beans 88 1854 4,846 30,110 58,950 12,626 3657
Pease 101 1332 2,873 36,715 62,780 5,281 ...
Clover 400 1645 2,948 50,100 .........

Table II.—Showing the average daily Loss of Water (in Grains) by the Plants, within several stated divisional Periods of their Growth

Description of Plant.9 Days.31 Days.27 Days.34 Days.30 Days.14 Days.27 Days.
From Mar. 19 to Mar. 28.From Mar. 28 to Apr. 28.From Apr. 28 to May 25.From May 25 to June 28.From June 28 to July 28.From July 28 to Aug. 11.From Aug. 11 to Sept. 7.
Wheat 14·3 40·9 162·4 1177·4 1535·3 1101·4 230·9
Barley 14·3 60·2 445·5 1102·3 1502·0 1217·6 237·5
Beans 9·7 59·8 179·5 885·6 1965·0 901·8 135·4
Peas 11·2 42·9 106·4 1079·8 2092·7 377·2 ...
Clover 44·4 53·0 109·2 1473·5 .........

Similar experiments were made with the same plants in soils to which certain manures had been added, and with results generally similar. Calculating from these experiments, we are led to the apparently anomalous conclusion that the quantity of water exhaled by the plants growing on an acre of land greatly exceeds the annual fall of rain; although it is obvious that of all the rain which falls, only a small proportion can be absorbed by the plants growing on the soil, for a large quantity is carried off by the rivers, and never reaches their roots. It has been calculated, for instance, that the Thames carries off in this way at least one-third of the annual rain that falls in the district watered by it, and the Rhine nearly four-fifths. Of course this large exhalation must depend on the repeated absorption of the same quantity of water, which, after being exhaled, is again deposited on the soil in the form of dew, and passes repeatedly through the plant. This constant percolation of water is of immense importance to the plant, as it forms the channel through which some of its other constituents are carried to it.

Carbonic Acid.—While the larger part of the water which a plant requires is absorbed by its roots, the reverse is the case with carbonic acid. A certain proportion no doubt is carried up through the roots by the water, which always contains a quantity of that gas in solution, but by far the larger proportion is directly absorbed from the air by the leaves. A simple experiment of Boussingault's illustrates this absorption very strikingly. He took a large glass globe having three apertures, through one of which he introduced the branch of a vine, with twenty leaves on it. With one of the side apertures a tube was connected, by means of which the air could be drawn slowly through the globe, and into an apparatus in which its carbonic acid was accurately determined. He found, in this way, that while the air which entered the globe contained 0·0004 of carbonic acid, that which escaped contained only 0·0001, so that three-fourths of the carbonic acid had been absorbed.

Ammonia and Nitric Acid.—Little is known regarding the mode in which these substances enter the plant. It is usually supposed that they are entirely absorbed by the roots, and no doubt the greater proportion is taken up in this way, but it is very probable that they may also be absorbed by the leaves, at least the addition of ammonia to the air in which plants are grown, materially accelerates vegetation. It is probable, however, that the rain carries down the ammonia to the roots, and there is no doubt that that derived from the decomposition of the nitrogenous matters in the soil is so absorbed.

Inorganic Constituents.—The inorganic constituents of course are entirely absorbed by the roots; and it is as a solvent for them that the large quantity of water continually passing through the plants is so important. They exist in the soil in particular states of combination, in which they are scarcely soluble in water. But their solubility is increased by the presence of carbonic acid contained in the water, and which causes it to dissolve, to some extent, substances otherwise insoluble. It is in this way that lime, which occurs in the soil principally as the insoluble carbonate, is dissolved and absorbed. And phosphate of lime is also taken up by water containing carbonic acid, or even common salt in solution. The amount of solubility produced by these substances is extremely small; but it is sufficient for the purpose of supplying to the plant as much of its mineral constituents as are required, for the quantity of water which, as we have already seen, passes through a plant is very large when compared with the amount of inorganic matters absorbed. It has been shown by Lawes and Gilbert, that about 2000 grains of water pass through a plant for every grain of mineral matter fixed in it, so that there is no difficulty in understanding how the absorption takes place.

It is worthy of notice, however, that the absorption of the elements of plants takes place even though they may not be in solution in the soil, the roots apparently possessing the power of directly acting on and dissolving insoluble matters; but a distinction must be drawn between this and the view entertained by Jethro Tull, who supposed that they might be absorbed in the solid state, provided they were reduced to a state of sufficient comminution. It is now no longer doubted that, whatever action the roots may exert, the constituents of the plant must be in solution before they can pass into it—experiment having distinctly shown that the spongioles or apertures through which this absorption takes place are too minute to admit even the smallest solid particle.

The Inorganic Constituents of Plants

When treating of the general constituents of plants, it has been already stated that the older chemists and vegetable physiologists, misled by the small quantity of ash found in them, entertained the opinion that mineral matters were purely fortuitous components of vegetables, and were present merely because they had been dissolved and absorbed along with the humus, which was then supposed to enter the roots in solution, and to form the chief food of the plant. This supposition, which could only be sustained at a time when analysis was imperfect, has been long since disproved and abandoned, and it has been distinctly shown by repeated experiment that not only are these inorganic substances necessary to the plant, but that every one of them, however small its quantity, must be present if it is to grow luxuriantly and arrive at a healthy maturity. The experiments of Prince Salm Horstmar, before alluded to, have established beyond a doubt, that while a seed may germinate, and even grow, to a certain extent, in absence of one or more of the constituents of its ash, it remains sickly and stunted, and is incapable of producing either flower or seed.

Of late years the analysis of the ash of different plants has formed the subject of a large number of laborious investigations, by which our knowledge of this subject has been greatly extended. From these it appears that the quantity of ash contained in each plant or part of a plant is tolerably uniform, differing only within comparatively narrow limits, and that there is a special proportion belonging to each individual organ of the plant. This fact may be best rendered obvious by the subjoined table, showing the quantity of ash contained in a hundred parts of the different substances dried at 212°. Most of these numbers are the mean of several experiments:—

Table showing the quantity of inorganic matters in 100 parts of different plants dried at 212°.

SEEDS.
Wheat 1·97
Barley 2·48
Oats (with husk)3·80
Oats (without husk)2·06
Rye 2·00
Millet 3·60
Rice 0·37
Maize 1·20
Peas 2·88
Beans 3·22
Kidney Beans 4·09
Lentils 2·51
Tares 2·60
Buckwheat 2·13
Linseed 4·40
Hemp seed 5·60
Rape seed 4·35
Indian Rape-seed [A]4·06
Sunflower 3·26
Cotton seed 5·93
Guinea Corn 1·99
Gold of Pleasure 4·10
White Mustard 4·15
Black Mustard 4·31
Poppy 6·56
Niger seed (Guizotia oleifera )7·00
Earth nut 3·88
Sweet Almond 4·90
Horse-chesnut 2·81
Grape 2·76
Clover 6·19
Turnip 3·98
Carrot 10·03
Sainfoin 5·27
Italian Ryegrass 6·91
Mangold-Wurzel 6·58
STRAWS AND STEMS.
Wheat 4·54
Barley 4·99
Oat 7·24
Winter Rye 5·15
Summer Rye 5·78
Millet 8·32
Maize 3·60
Pea 4·81
Bean 6·59
Tares 6·00
Lentil 5·38
Buckwheat 4·50
Hops 4·42
Flax straw 4·25
Hemp 4·14
Gold of Pleasure 6·05
Rape 4·41
Potato 14·90
Jerusalem Artichoke 4·40
ENTIRE PLANT.
Potato 17·70
Spurry 10·06
Red Clover 8·79
White Clover 8·72
Yellow Clover 8·56
Crimson Clover (T. incarnatum )10·81
Cow Grass (T. medium )11·31
Sainfoin 6·51
Ryegrass 6·42
Meadow Foxtail (Alopecurus pratensis )7·81
Sweet-scented Vernal Grass (Anthoxanthum odoratum )6·32
Downy Oat Grass (Avena pubescens )5·22
Bromus erectus 5·21
Bromus mollis 5·82
Cynosurus cristatus 6·38
Dactylis glomeratus 5·31
Festuca duriuscula 5·42
Holcus lanatus 6·37
Hordeum pratense 5·67
Lolium perenne 7·54
Poa annua 2·83
Poa pratensis 5·94
Poa trivialis 8·33
Phleum pratense 5·29
Plantago lanceolata 8·68
Poterium Sanguisorba 7·97
Yarrow 13·45
Rape Kale 8·00
Cow Cabbage 10·00
Asparagus 6·40
Parsley 1·10
Furze 3·11
Chamomile (Anthemis arvensis )9·66
Wild Chamomile (Matricaria Chamomilla )9·10
Corn Cockle (Agrostemma Githago )13·20
Corn Blue Bottle (Centaurea Cyanus )7·32
Foxglove 10·89
Hemlock (Conium maculatum )12·80
Sweet Rush (Acorus Calamus )6·90
Common Reed (Arundo Phragmites )1·44
Celandine (Chelidonium majus )6·85
Equisetum fluviatile 23·60
Equisetum hyemale 11·80
     "        arvense 13·80
     "        linosum 15·50
Fucus nodosus 19·03
Fucus vesiculosus 27·63
Laminaria digitata 39·68
LEAVES.
Turnip 9·37
Beet 20·30
Kohl-rabi 18·54
Carrot 10·95
Jerusalem Artichoke 28·30
Hemp 22·00
Hop 17·25
Tobacco 22·62
Spinach 19·76
Chicory 15·67
Poplar 23·00
Red Beech 6·00
White Beech 10·51
Oak 9·80
Elm 16·33
Horse-chesnut 9·08
Maple 28·05
Ash 14·76
Fir 2·31
Acacia 18·20
Olive 6·45
Orange 13·73
Potato 15·10
Tussac Grass 7·15
ROOTS AND TUBERS.
Potato 4·16
Jerusalem Artichoke 5·38
Turnip 13·64
Beet 8·27
Kohl-rabi 6·08
Rutabaga 7·34
Carrot 5·80
Belgian White Carrot 6·22
Mangold-Wurzel 8·78
Parsnip 5·52
Radish 7·35
Chicory 5·21
Madder 8·33
WOODS.
Beech 0·38
Apple 1·29
Cherry 0·28
Birch 1·00
Oak 2·50
Walnut 1·57
Lime 5·00
Horse-chesnut 1·05
Olive 0·58
Mahogany 0·81
Vine 2·57
Larch 0·32
Fir 0·14
Scotch Fir 0·17
Filbert 0·50
Chesnut 3·50
Poplar 0·80
Hazel 0·50
Orange 2·74
Vine 2·57
BARKS.
Beech 6·62
Cherry 10·37
Fir 1·79
Oak 6·00
Horse-chesnut 7·85
Filbert 6·20
Cork 1·12
FRUITS.
Plum 0·40
Cherry 0·43
Strawberry 0·41
Pear 0·41
Apple 0·27
Chesnut 0·99
Cucumber 0·63
Vegetable Marrow 5·10

On examining this table it may be observed that, notwithstanding the very great variety in the proportion of ash in different plants, some general relations may be traced. A certain similarity may be observed between those belonging to the same natural family, the seeds of all the cereal grains, for instance, containing in round numbers two per cent of inorganic matters. Leguminous seeds (peas and beans) contain about three per cent, while in rape-seed, linseed, and the other oily seeds, it reaches four per cent. In the stems and straws less uniformity exists, but with the exception of a few extreme cases, the quantity of ash in general approaches pretty closely to five per cent. Still more diversified results are obtained from the entire plants; but this diversity is probably much more apparent than real, and must be, in part at least, dependent on the proportion existing between the stem and leaves, for the leaves are peculiarly rich in ash, and a leafy plant must necessarily yield a higher total percentage of ash, although, if stems and leaves were separately examined, they might not show so conspicuous a difference.

The leaves surpass all other parts of plants, in the proportion of inorganic constituents they contain, the table showing that in some instances, as in the maple and Jerusalem artichoke, they exceed one-fourth of the whole weight of the dry matter. In other leaves, and more especially in those of the coniferæ, the proportion is much smaller. Taking the average of all the analyses hitherto made, it appears that leaves contain about thirteen per cent of ash, but the variations on either side are so large that little value is to be attached to it except as an indication of the general abundance of mineral matters.

In roots and tubers the variations are less, and all, except the potato and the turnip, contain about seven per cent of ash.

The smallest proportion of mineral matter is found in wood. In one case only does the proportion reach five per cent, while the average scarcely exceeds one, and in the fir the quantity amounts to no more than one six-hundredth of the dry matter. In the bark the quantity is much larger, and may be stated at seven per cent.

The general proportion of ash found in different parts of plants is given in round numbers in the subjoined table:—

Wood 1
Seeds 3
Stems and straws 5
Roots and tubers 7
Bark 7
Leaves 13

The differences in the quantity of ash contained in different parts of plants are obviously intended to serve a useful purpose, and it is interesting to observe that the wood which is destined to remain for a long period, sometimes for several centuries, a part of the plant, contains the smallest proportion, and it is not improbable that what it does contain is really due, not to the actual woody matter itself, but to the sap which permeates its vessels. By this arrangement but a small proportion of these important mineral matters, which the soil supplies in very limited quantity, is locked up within the plant, and those which are absorbed, after circulating through it, and fulfilling their allotted functions, are accumulated in the leaves, and annually returned to the soil.

The different proportions of mineral matters contained in the individual organs of plants is most strikingly illustrated when parallel experiments are made on the same species; but the number of instances in which a sufficiently extensive series of analyses has been made to show this, is comparatively limited, and is confined to the oat, the orange-tree, and the horse chesnut—each of which has formed the subject of a very elaborate investigation. The following table gives the results obtained on the oat:—

 Hopetoun Oats, Northumberland.Hopetoun Oats, Fifeshire.Potato Oats, Northumberland.Black Oats, Edinburgh.Sandy Oats, Fifeshire.Mean.
Grain 2·14 1·81 2·22 2·11 1·76 2·00
Husk 6·47 6·03 6·99 8·24 6·03 6·75
Chaff 16·53 17·23 15·59 19·19 18·97 16·06
Leaves 8·44 7·19 14·59 10·29 15·92 10·88
Upper part of straw 4·95 5·44 9·22 8·25 11·0 7·77
Middle part of straw 6·11 5·23 7·41 6·53 9·01 6·66
Lower part of straw 5·33 5·18 9·76 7·11 7·30 6·93

The specimens of oats on which these analyses were made were from different districts of country, grown on soils of different quality, and were, further, of different varieties; and yet they show, on the whole, a remarkable similarity in the proportion of ash in each part, and indicate that there is a normal quantity belonging to it. Such a series of analyses also affords the most convincing proof that the inorganic matters cannot be fortuitous, and merely absorbed from the soil along with their organic food, as the old chemists supposed, because, in that case, they ought to be uniformly distributed throughout the entire plant, and not accumulated in particular proportions in each individual organ.

Not only does the proportion of ash vary in the different parts of a plant, but even in the same part it is greatly influenced by its period of growth. The laws which regulate these variations are very imperfectly known, but in general it is observed that during the period of active growth the quantity of ash is largest. Thus, it has been found that in early spring the wood of the young shoots of the horse-chesnut contains 9·9 per cent of ash. In autumn this has diminished to 3·4, and the last year's twigs contain only 1·1 per cent, while in the old wood the quantity does not exceed 0·5. Saussure has also observed that the quantity of ash diminishes in certain plants when the seed has ripened. Thus, he found that the percentages of ash, before flowering, and after seeding, were as follows:—

Before flowering.With ripe seed.
Sunflower 14·7 9·3
Wheat 7·9 3·3
Maize 12·2 4·6

On the other hand, the quantity of ash in the leaves of trees increases considerably in autumn, as shown by this table:—

Per-centage of ash in
May.September.
Oak leaves 5·3 5·5
Poplar 6·6 9·3
Hazel 6·1 7·0
Horse-chesnut 7·2 8·6

In general, the proportion of ash appears to increase as the plant reaches maturity, and this is particularly seen in the oat, of which very complete analyses have been made at different periods of its growth:—

Proportion of Ash in different parts of the Oat at different periods of its growth

Date.Stalks.Leaves.Chaff.Grain with husk.
2d July 7·83 11·35 ...4·91
9th July 7·80 12·20 ...4·36
16th July 7·94 12·61 6·00 3·38
23d July 7·99 16·45 9·11 3·62
30th July 7·45 16·44 12·28 4·22
5th August 7·63 16·05 13·75 4·31
13th August 6·62 20·47 18·68 4·07
20th August 6·66 21·14 21·07 3·64
27th August 7·71 22·13 22·46 3·51
3d September 8·35 20·90 27·47 3·65

The increase is here principally confined to the leaves and chaff, while the stalks, which owe their strength to a considerable extent to the inorganic matters they contain, are equally supplied at all periods of their growth. In the grain only is there a diminution, but this is apparent and not real, and is due to the fact that the determination of the quantity of ash, as made on the grain with its husk, and the former, which contains only a small quantity of mineral matters, increases much more rapidly in weight than the latter, when it approaches the period of ripening, and it is accordingly during the last three weeks of its growth that this diminution becomes apparent.

The nature of the soil has also a very important influence on the proportion of mineral matters, and of this an interesting illustration is given in the following table, which shows the quantities found in the grain and straw of the same variety of the pea grown on fourteen different soils:—

 Seed.Straw.
1 2·30  
2 3·25 3·43
3 4·27 3·62
4 3·40 3·39
5 2·99 3·90
6 3·19 6·80
7 2·53 3·90
8 2·27 6·59
9 2·69 3·49
10 1·61 3·91
11 3·11 5·28
12 3·34 7·57
13 2·78 3·76
14 3·01 3·38

Although those differences are very large, especially in the straw, and must be attributed to the soil, it has hitherto been found impossible to ascertain the nature of the relation subsisting between it and the crops it yields; indeed, it must obviously be dependent on very complicated questions, which cannot at present be solved, for it may be observed that the increase in the grain does not occur simultaneously with that in the straw, and in several cases a large proportion of ash in the former is associated with an unusually small amount in the latter. A priori, it might be expected that those soils which are especially rich in the more important constituents of the ash should yield a produce containing more than the average quantity, but this is very far from being an invariable occurrence, and not unfrequently the very reverse is the case. In some instances the variations may be traced to the soil, as in the following analyses of the fruit of the horse-chesnut, grown on an ordinary forest soil, and on a rich soil, produced by the disintegration of porphyritic rock, in which the latter yields a much larger quantity of ash:—

Kernel of seed.Green husk.Brown husk.
Forest soil 2·26 4·53 1·70
Porphyry soil 3·36 7·29 2·20

In the majority of instances we fail to establish any connection between the nature of the soil and the plants it yields, chiefly because we are still very deficient in analyses of those grown on uncultivated soils; and on cultivated land it is impossible to draw conclusions, because the nature of the manure exerts an influence quite as great, if not greater, than that of the soil itself.

The relative proportion in which the different mineral matters enter into the composition of the ash varies within very wide limits, as will be apparent from the following table, containing a selection of the best analyses of our common cultivated and a few uncultivated plants.

Table of the Composition of the Ash of different Plants in 100 Parts

Note.—Alumina and oxide of manganese occur so rarely, that separate columns have not been introduced for them, but their quantity is stated in notes at the end of the table.

 Potash.Soda.Chloride of Potassium.Chloride of Sodium.Lime.Magnesia.
Wheat, grain 30·02 3·82 ......1·15 13·39
    straw 17·98 2·47 ......7·42 1·94
    chaff 9·14 1·79 ......1·88 1·27
Barley, grain 21·14 ...5·65 1·01 1·65 7·26
    straw 11·22 ......2·14 5·79 2·70
Oats, grain [B]20·63 ...1·03 ...10·28 7·82
    straw 19·46 1·93 2·71 4·27 7·01 3·79
    chaff [C]6·33 3·93 ...0·24 1·95 0·38
Rye, grain 33·83 0·39 ......2·61 12·81
    straw 17·20 ...0·30 0·60 9·10 2·40
Maize, grain 28·37 1·74 ...trace 0·57 13·60
    stalks and leaves 35·26 ......2·29 10·53 5·52
Rice, grain 20·21 2·49 ......7·18 4·26
Buckwheat, straw 31·71 ...7·42 4·55 15·71 1·66
Peas (gray), seed 41·70 ...3·82 1·24 4·78 5·78
    straw 21·30 4·22 ......37·17 7·17
Beans (common field),      
    grain 51·72 0·54 ......5·20 6·90
    straw 32·85 2·77 ...11·54 19·85 2·53
Tare, straw 32·82 ...3·27 4·03 20·78 5·31
    straw 31·72 ...7·41 4·55 15·71 1·66
Flax, seed 34·17 1·69 ...0·36 8·40 13·11
    straw 21·53 3·68 ...9·21 21·20 4·20
Rape, seed [D]16·33 0·34 ...0·96 8·30 8·80
    straw [E]16·63 10·57 ...2·53 21·51 2·92
Spurry 26·12 1·14 ...8·90 14·46 8·88
Chicory root 34·64 ...8·92 2·98 ......
Red clover 25·60 ...9·08 6·02 21·57 8·47
Cow grass, Trifolium medium 22·78 ...12·39 1·86 24·42 8·86
Yellow clover 27·48 ...11·72 8·16 17·26 8·39
Alsike clover 29·72 ...6·29 1·05 26·83 4·01
Lucerne 27·56 ...11·64 1·91 20·60 5·22
Anthoxanthum odoratum 32·03 ...7·03 4·90 9·21 2·53
Alopecurus pratensis 37·03 ...9·50 ...3·90 1·28
Avena pubescens 31·21 ...4·05 5·66 4·72 3·17
Bromus erectus 20·33 ...10·63 1·38 10·38 4·99
Bromus mollis 30·09 0·33 ...3·11 6·64 2·60
Cynosurus cristatus 24·99 ...11·60 ...10·16 2·43
Dactylis glomerata 29·52 ...17·86 3·09 5·82 2·22
Festuca duriuscula 31·84 ...8·17 0·62 10·31 2·83
Holcus lanatus 34·83 ...3·91 6·66 8·31 3·41
Lolium perenne 24·67 ...13·80 7·25 9·64 2·85
Annual ryegrass 28·99 0·87 ...5·11 6·82 2·59
Poa annua 41·86 ...0·47 3·35 11·69 2·44
Poa pratensis 31·17 ...11·25 1·31 5·63 2·71
Poa trivialis 29·40 ...6·90 ...8·80 3·22
Phleum pratense 31·09 ...0·70 3·24 14·94 5·30
Plantago lanceolata 33·26 ...4·53 8·80 19·01 3·51
Poterium Sanguisorba 30·26 ...3·27 1·35 24·82 4·21
Achillea Millefolia 30·37 ...20·49 3·63 13·40 3·01
Potato, tuber 43·18 0·09 ...7·92 1·80 3·17
    stem 39·53 3·95 ...20·43 14·85 4·10
    leaves 17·27 ...4·95 11·37 27·69 7·78
Jerusalem Artichoke 55·89 ...4·88 ...3·34 1·30
    stem 38·40 0·69 ...4·68 20·31 1·91
    leaves 6·81 3·72 ...1·82 40·15 1·95
Turnip, seed 21·91 1·23 ......17·40 8·74
    bulb 23·70 14·75 ...7·05 11·82 3·28
    leaves 11·56 12·43 ...12·41 28·49 2·62
Mangold Wurzel, root 21·68 3·13 ...49·51 1·90 1·79
    leaves 8·34 12·21 ...37·66 8·72 9·84
Carrot, root 42·73 12·11 ......5·64 2·29
    leaves 17·10 4·85 ...3·62 24·05 0·89
Kohl-rabi, bulb 36·27 2·84 ...11·90 10·20 2·36
    leaves 9·31 ...5·99 6·66 30·31 3·62
Cow cabbage, head 40·86 2·43 ......15·01 2·39
    stalk 40·93 4·05 ...2·08 10·61 3·85
Poppy seed 9·10 ...7·15 1·94 35·36 9·49
    leaves 36·37 ...2·50 2·51 30·24 6·47
Mustard seed (white)25·78 0·33 ......19·10 5·90
Radish root 21·16 ...1·29 7·07 8·78 3·53
Tobacco leaves 36·37 ...2·50 2·51 30·24 6·47
Fucus nodosus [F]20·03 4·58 ...24·33 9·60 6·65
Fucus vesiculosus [G]20·75 6·09 ...24·81 8·92 5·83
Laminaria digitata [H]12·16 ...2·30 19·34 4·62 10·94




 Oxide of Iron.Phosphoric Acid.Sulphuric Acid.Carbonic Acid.Silica.
Wheat, grain 0·91 46·79 ......3·89
    straw 0·45 2·75 3·09 ...63·89
    chaff 0·37 4·31 ......81·22
Barley, grain 2·13 28·53 1·91 ...30·68
    straw 1·36 7·20 1·09 ...68·50
Oats, grain 3·85 50·44 ......4·40
    straw 1·49 5·07 3·35 1·36 49·56
    chaff 1·58 1·04 9·61 ...72·85
Rye, grain 1·04 39·92 0·17 ...9·22
    straw 1·40 3·80 0·80 ...64·50
Maize, grain 0·47 53·69 ......1·55
    stalks and leaves 2·28 8·09 5·16 2·87 27·98
Rice, grain 2·12 62·23 ......1·37
Buckwheat, straw ...10·34 4·67 20·37 3·57
Peas (gray), seed 0·18 36·50 4·47 0·82 0·68
    straw 1·07 4·65 8·68 12·48 3·23
Beans (common field),     
    grain ...28·72 3·05 3·42 0·42
    straw 0·61 0·49 1·40 25·32 2·61
Tare, straw 0·65 10·59 2·52 18·73 1·28
    straw ...10·34 4·67 20·37 3·57
Flax, seed 0·50 38·54 1·56 0·22 1·45
    straw 5·58 7·53 3·39 15·75 7·92
Rape, seed 1·79 31·90 5·38 5·44 19·98
    straw 1·30 4·68 3·90 23·04 11·80
Spurry ...10·20 1·79 27·38 1·14
Chicory root ...............
Red clover 1·26 4·09 2·96 18·05 1·95
Cow grass, Trifolium medium 1·09 4·94 2·66 20·16 1·12
Yellow clover 1·40 ...4·82 4·31 1·76
Alsike clover 0·71 5·64 3·25 20·74 1·73
Lucerne 2·23 6·47 4·80 15·94 2·63
Anthoxanthum odoratum 1·18 10·09 3·39 1·26 28·35
Alopecurus pratensis 0·47 6·25 2·16 0·65 38·75
Avena pubescens 0·72 10·82 3·37 ...36·28
Bromus erectus 0·26 7·53 5·46 0·55 38·48
Bromus mollis 0·28 9·62 4·91 9·07 33·34
Cynosurus cristatus 0·18 7·24 3·20 ...40·11
Dactylis glomerata 0·59 8·60 3·52 2·09 26·65
Festuca duriuscula 0·78 12·07 3·45 1·38 28·53
Holcus lanatus 0·31 8·02 4·41 1·82 28·31
Lolium perenne 0·21 8·73 5·20 0·49 27·13
Annual ryegrass 0·28 10·07 3·45 ...41·79
Poa annua 1·57 9·11 10·18 3·29 16·03
Poa pratensis 0·28 10·02 4·26 0·40 32·93
Poa trivialis 0·29 9·13 4·47 0·29 37·50
Phleum pratense 0·27 11·29 4·86 4·02 31·09
Plantago lanceolata 0·90 7·08 6·11 14·40 2·37
Poterium Sanguisorba 0·86 7·81 4·84 21·72 0·83
Achillea Millefolia 0·21 7·13 2·44 9·36 9·92
Potato, tuber 0·44 8·61 15·24 18·29 1·94
    stem 1·34 6·68 6·56 ...2·56
    leaves 4·50 13·60 6·37 ...6·47
Jerusalem Artichoke 0·45 16·99 3·77 11·80 1·52
    stem 0·88 2·97 3·23 25·40 1·51
    leaves 1·14 6·61 2·21 24·31 17·25
Turnip, seed 1·95 40·17 7·10 0·82 0·67
    bulb 0·47 9·31 16·13 10·74 2·69
    leaves 3·02 4·85 10·36 6·18 8·04
Mangold Wurzel, root 0·52 1·65 3·14 15·23 1·40
    leaves 1·46 5·89 6·54 6·92 2·35
Carrot, root 0·51 12·31 4·26 18·00 1·11
    leaves 3·43 6·21 5·08 23·15 11·61
Kohl-rabi, bulb 0·38 13·45 11·43 10·24 0·83
    leaves 5·50 9·43 10·63 8·97 9·57
Cow cabbage, head 0·77 12·53 7·27 16·68 1·66
    stalk 0·41 19·57 11·11 6·33 1·04
Poppy seed 0·41 31·38 1·92 ...3·24
    leaves 2·14 3·28 5·09 ...11·40
Mustard seed (white)0·39 44·97 2·19 ...1·31
Radish root 1·19 41·09 7·71 ...8·17
Tobacco leaves 2·18 3·24 5·09 ...11·40
Fucus nodosus 0·26 1·71 21·97 6·39 0·38
Fucus vesiculosus 0·35 2·14 28·01 2·20 0·67
Laminaria digitata 0·45 1·75 7·26 15·23 1·20

A simple inspection of this table leads to various interesting conclusions. It is particularly to be observed that some of the constituents of the ash are not invariably present, and two at least—namely, alumina and manganese—are found so rarely as to justify the inference that they are not indispensable. Of the other substances, iodine is restricted exclusively to sea-plants, but to them it appears to be essential. Oxide of iron, which occurs only in small quantities, has sometimes been considered fortuitous, but it is almost invariably present, and the experiments of Prince Salm Horstmar leave no doubt that it is essential to the plant. Its function is unknown, but it is an important constituent of the blood of herbivorous animals, and may be present in the plant, less for its own benefit than for that of the animal of which it is destined to become the food.

Soda appears to be a comparatively unimportant constituent of the ash, of which it generally forms but a small proportion, although the instances of its entire absence are rare. In the cruciferous plants (turnip, rape, etc.) it is found abundantly, and to them it appears indispensable, but in most other plants it admits of replacement by potash. It seems probable that where the soil is rich in the latter substance, plants will select that alkali in preference to soda; but as they must have a certain quantity of alkali, the latter may supply the place of the former where it is deficient. Cultivation, probably by enriching the soil in that element, increases the proportion of potash found in the ash of plants, as is remarkably seen in the asparagus, which gave the following quantities of alkalies and chlorine:—

Wild.Cultivated.
Potash 18·8 50·5
Soda 16·2 trace.
Chlorine 16·5 8·3

The soda having almost entirely disappeared in the cultivated plant, while a corresponding increase had taken place in the quantity of potash.

Potash is one of the most important elements of the ash of all plants, rarely forming less than 20, and sometimes more than 50 per cent of its weight. The latter proportion occurs chiefly in the roots and tubers, but it is also abundant in all seeds and in the grasses. The straw, and particularly the chaff of the cereals, and the leaves of most plants, contain it in smaller quantity, although exceptions to this are not unfrequent, one of the most curious being the case of poppy-seed, which contains only about 12 per cent, while the leaves yield upwards of 37 per cent.

The proportion of lime varies within very wide limits, being sometimes as low as 1, and in other plants reaching 40 per cent of their ash. The former proportion occurs in the grains of the cerealia, and the latter in the leaves of some plants, and more especially in the Jerusalem artichoke. The turnip and some of the leguminous plants also contain it abundantly.

Magnesia is generally found in small quantity. It is largest in the grains, amounting in them to about 12 or 13 per cent of the ash, but in other plants it varies from 2 to 4 per cent. Although small in quantity, it is an important substance, and apparently cannot be dispensed with; at least there is no instance known of its entire absence.

Chlorine  is by no means an invariable constituent of the ash, although it is generally present, and sometimes in considerable quantity. It is most abundant when the proportion of soda is large, and exists in the ash principally in combination with that base as common salt. The relation between these two elements may be traced more or less distinctly throughout the whole table of analyses, and conspicuously in that of mangold-wurzel, where the common salt amounts to almost exactly one-half of the whole mineral matter. The analyses of the cultivated and uncultivated asparagus also show that a diminution in the soda is accompanied by a reduction in the proportion of chlorine.

Sulphuric Acid  is an essential constituent of the ash. But it is to be observed that it is in some instances entirely, and in all partially, a product of the combustion to which the plant has been submitted in order to obtain the ash. It is partly derived from the sulphur contained in the albuminous compounds, which is oxidised and converted into sulphuric acid during the process of burning the organic matter, and remains in the ash. The quantity of sulphuric acid found in the ash is, however, no criterion of that existing in the plant, for a considerable quantity of it escapes during burning. The extent to which this occurs in particular instances is well illustrated by reference to the case of white mustard, which yields an ash containing only 2·19 of sulphuric acid, equivalent to 0·9 of sulphur; and if calculated on the seed itself, this will amount to no more than 0·039 per cent, while experiments made in another manner prove it to contain about thirty times as much, or more than 1 per cent. For the purpose of determining the total quantity of sulphur which the plants contain in their natural state, it is necessary to oxidise them by means of nitric acid; and from such experiments the following table, showing the total  amount of sulphur contained in 100 parts of different plants, dried at 212°, has been constructed:—

Poa palustris 0·165
Lolium perenne 0·310
Italian Ryegrass 0·329
Trifolium pratense 0·107
    repens 0·099
Lucerne 0·336
Vetch 0·178
Potato tuber 0·082
    tops 0·206
Carrot, root 0·092
    tops 0·745
Mangold-Wurzel, root 0·058
    tops 0·502
Swede, root 0·435
    tops 0·458
Rape 0·448
Drumhead Cabbage 0·431
Wheat, grain 0·068
    straw 0·245
Barley, grain,0·053
    straw 0·191
Oats, grain 0·103
    straw 0·289
Rye, grain 0·051
Beans 0·056
Peas 0·127
Lentils 0·110
Hops 1·063
Gold of Pleasure 0·253
Black Mustard 1·170
White Mustard 1·050

Phosphoric acid, which may be looked upon as the most important mineral constituent of plants, is found to be present in very variable proportions. The straws, stems, and leaves contain it in comparatively small quantity, but in the seeds of all plants it is very abundant. In these of the cereals it constitutes nearly half of their whole mineral components, and it rarely falls below 30 per cent.

Carbonic acid  occurs in very variable quantities in the ash. It is of comparatively little importance in itself, and is really produced by the oxidation of part of the carbonaceous matters of the plant; but it has a special interest, in so far as it shows that part of the bases contained in the plant must in its natural state have been in union with organic acids, or combined in some way with the organic constituents of the plant.

Silica  is an invariable constituent of the ash, but in most plants occurs but in small quantity. The cereals and grasses form an exception to this rule, for in them it is an abundant and important element. It is not, however, uniformly distributed through them, but is accumulated to a large extent in the stem, to the strength and rigidity of which it greatly contributes. The hard shining layer which coats the exterior of straw, and which is still more remarkably seen on the surface of the bamboo, consists chiefly of silica; and in the latter plant this element is sometimes so largely accumulated, that concretions resembling opal, and composed entirely of it, are found loose within its joints. The necessity for a large supply of silica in the stems of other plants does not exist, and in them it rarely exceeds 5 or 6 per cent, but in some leaves it is more abundant.

A knowledge of the composition of the ash of plants is of considerable importance in a practical point of view, and enables us in many instances to explain why some plants will not grow upon particular soils on which others flourish. Thus, for instance, a plant which contains a large quantity of lime, such as the bean or turnip, will not grow in a soil in which that element is deficient, although wheat or barley, which require but little lime, may yield excellent crops. Again, if the soil be deficient in phosphoric acid, those plants only will grow luxuriantly which require but a small quantity of that element, and hence it follows that on such a soil plants cultivated for the sake of their stems, roots, or leaves, in which the quantity of phosphoric acid is small, may yield a good return; while others, cultivated for the sake of their seed, in which the great proportion of that constituent of the ash is accumulated, may yield a very small crop. It is obvious also that even where a soil contains a proper quantity of all its ingredients, the repeated cultivation of a plant which removes a large quantity of any individual element, may, in the course of time, so far reduce the amount of that substance as to render the soil incapable of any longer producing that plant, although, if it be replaced by another which requires but little of the element thus removed, it may again produce an abundant crop. On this principle also, attempts have been made to explain the rotation of crops, which has been supposed to depend on the cultivation in successive years of plants which abstract from the soil preponderating quantities of different mineral matters. But though this has unquestionably a certain influence, we shall afterwards see reason to doubt whether it affords a sufficient explanation of all the observed phenomena.

It may be observed, on examining the table of the percentage and position of the ash, that some plants are especially rich in alkalies, while in others lime or silica preponderate, and it would therefore be the object of the farmer to employ, in succession, crops containing these elements in different proportions. In carrying out this view, attempts have been made to classify different plants under the heads of silica plants, lime plants, and potash plants; and the following table, extracted from Liebig's Agricultural Chemistry, in which the constituents of the ash are grouped under the three heads of salts of potash and soda, lime and magnesia, and silica, gives such a classification as far as it is at present possible:—

  Salts of Potash and Soda.Salts of Lime and Magnesia.Silica.
Silica Plants.Oat straw with seeds 34·00 4·00 62·00
Wheat straw 22·50 7·20 61·50
Barley straw with seeds 19·00 25·70 55·30
Rye straw 18·65 16·52 63·89
Good hay 6·00 34·00 60·00
Lime Plants Tobacco 24·34 67·44 8·30
Pea straw 27·82 63·74 7·81
Potato plant 4·20 59·40 36·40
Meadow Clover 39·20 56·00 4·90
Potash Plants.Maize straw 72·45 6·50 18·00
Turnips 81·60 18·40
Beet root 88·00 12·00
Potatoes 85·81 14·19
Jerusalem Artichoke 84·30 15·70

The special application of these facts must be reserved till we come to treat of the rotation of crops.

It is manifest that, as the crops removed from the soil all contain a greater or less amount of inorganic matters, they must be continually undergoing diminution, and at length be completely exhausted unless their quantity is maintained from some external source. In many cases the supply of these substances is so large that ages may elapse before this becomes apparent, but where the quantity is small, a system of reckless cropping may reduce a soil to a state of absolute sterility. A remarkable illustration of this fact is found in the virgin soils of America, from which the early settlers reaped almost unheard-of crops, but, by injudicious cultivation, they were soon exhausted and abandoned, new tracts being brought in and cultivated only to be in their turn abandoned. The knowledge of the composition of the ash of plants assists us in ascertaining how this exhaustion may be avoided, and indicates the mode in which such soils may be preserved in a fertile state.

Footnotes:

[A]Apparently a species of Sinapis.

[B]Oxide of Manganese, 0·42.

[C]Oxide of Manganese, 0·92.

[D]Alumina, 1·02.

[E]Alumina, 0·63.

[F]Iodide of Potassium, 0·44; Sulphuret of Sodium, 3·66.

[G]Iodide of Potassium, 0·23.

[H]Iodide of Potassium, 1·68.