Plant skeleton

Plants, as well as animals, are organised bodies, and like them their parts may be dissected and decomposed by art; but the anatomy of the former has not been cultivated so long and with so much zeal and success as that of animals. Some naturalists, about the beginning of the last century, first began to make it an object of attention, to compare the structure of plants with that of animals; and for that purpose to employ the microscope. Among these, two distinguished themselves in a particular manner; Marcellus Malpighi, an Italian; and Nehemiah Grew, an Englishman; who both undertook almost the same experiments and made them known at the same time; so that it is impossible to determine which of them was the earlier. It appears, however, that Grew published some of his observations a little sooner; but Malpighi was prior in making his known in a complete manner. But even allowing that the one had received hints of the processes of the other, they are both entitled to praise that each made experiments of his own, and from these prepared figures, which are always more correct the nearer they correspond with each other.

Among the various helps towards acquiring a knowledge of the anatomy of plants, one of the principal is the art of reducing to skeletons leaves, fruit and roots; that is, of freeing them from their soft, tender and pulpy substance, in such a manner, that one can survey alone their internal, harder vessels in their entire connexion. This may be done by exposing the leaves to decay for some time soaked in water, by which means the softer parts will be dissolved, or at least separated from the internal harder parts, so that one, by carefully wiping, pressing and rinsing them, can obtain the latter alone perfectly entire. One will possess then a tissue composed of innumerable woody threads or filaments, which, in a multiplicity of ways, run through and intersect each other. By sufficient practice and caution one may detach, from each side of a leaf, a very thin covering, between which lies a delicate web of exceedingly tender vessels. These form a woody net-work, between the meshes of which fine glandules are distributed. This net is double, or at least can be divided lengthwise into halves, between which may be observed a substance that appears as it were to be the marrow of the plant. Persons who are expert often succeed so far, with many leaves, as to separate the external covering on both sides from the woody net, and to split the latter into two, so that the whole leaf seems to be divided into four.

One might conjecture that this method of reducing leaves to skeletons must have been long known, as one frequently finds in ponds leaves which have dropped from the neighbouring trees, and which by decomposition, without the assistance of art, have been converted into such a woody net-work, quite perfect and entire. It is however certain that a naturalist, about the year 1645, first conceived the idea of employing decomposition for the purpose of making leaf-skeletons, and of assisting it by ingenious operations of art.

This naturalist, Marcus Aurelius Severinus, professor of anatomy and surgery at Naples, was born in 1580, and died of the plague in 1656. In his Zootomia Democritæa, printed in 1645, he gave the figure, with a description of a leaf of the Ficus Opuntia  reduced to a skeleton. Of the particular process employed to prepare this leaf, the figure of which is very coarse and indistinct, he gives no account. He says only that the soft substance was so dissolved that the vessels or nerves alone remained; and that he had been equally successful with a leaf of the palm-tree. A piece of a leaf of the like kind he sent by Thomas Bartholin to Olaus Wormius, who caused it to be engraved on copper, in a much neater manner, without saying anything of the method in which it had been prepared 477. The process Severin kept secret; but he communicated it to Bartholin, in a letter, on the 25th of February 1645, on condition that he would not disclose it to any one. At that period, however, it excited very little attention, and was soon forgotten, though in the year 1685 one Gabriel Clauder made known that he had reduced vine-leaves, the calyx of the winter cherry, and a root of hemlock, to a net or tissue by burying them in sand during the heat of summer, and hanging them up some months in the open air till they were completely dried.

This art was considered to be of much more importance when it was again revived by the well-known Dutchman, Frederick Ruysch. That naturalist found means to conduct all his undertakings and labours in such a manner as to excite great wonder; but we must allow him the merit of having brought the greater part of them to a degree of perfection which no one had attained before. By the anatomy of animals, in which he was eminently skilled, he was led to the dissection of plants; and as it seemed impossible to fill their tender vessels, like those of animals, with a coloured solid substance 478 , he fell upon a method of separating the hard parts from the soft, and of preserving them in that manner.

For this purpose he first tried a method which he had employed with uncommon success, in regard to the parts of animals. He covered the leaves and fruit with insects, which ate up the soft or pulpy parts, and left only those that were hard. But however well these insects, which he called his little assistants, may have executed their task, they did not abstain altogether from the solid parts, so that they never produced a complete skeleton. He dismissed them, therefore, and endeavoured to execute with his own fingers what he had before caused the insects to perform, after he had separated the soft parts from the hard by decomposition. In this he succeeded so perfectly, that all who saw his skeletons of leaves or fruit were astonished at the fineness of the work and wished to imitate them.

I cannot exactly determine the year in which Ruysch began to prepare these skeletons. Trew thinks that it must have been when he was in a very advanced age, or at any rate after the year 1718; for when he was admitted to Ruysch's collection in that year, he observed none of these curiosities. Rundmann, however, saw some of them in his possession in the year 1708 479. At first Ruysch endeavoured to keep the process a secret, and to evade giving direct answers to the questions of the curious. We are informed by Rundmann, that he attempted to imitate his art by burying leaves at the end of harvest in the earth, and leaving them there till the spring, by which their soft parts became so tender that he could strip them off with the greatest ease. He produced also the same effect by boiling them.

The first account which Ruysch himself published of his process, was, as far as I know, in the year 1723. After he had sufficiently excited the general curiosity, he gave figures of some of his vegetable skeletons, related the whole method of preparing them, and acknowledged that he had accidentally met with an imperfect engraving of a leaf-skeleton in the Museum of Wormius, which had at one time occasioned much wonder 480. It is not improbable that he knew how the Italian, whom he does not mention, though he is mentioned by Wormius, and though he must certainly have been acquainted with his Zootomia, prepared his skeletons. I must however observe, that it is remarked by those who knew Ruysch, that he had read few books, and was very little versed in the literature of his profession.

In the year following, Ruysch described more articles of the like kind, and gave figures of some pears prepared in this manner. In 1726, when Vater, professor at Wittenberg, expressed great astonishment at the fineness of his works, he replied, in a letter written in 1727, that he had at first caused them to be executed by insects, but that he then made them himself with his fingers 481. He repeated the same thing also in 1728, when he described and gave engravings of more of these curious objects 482. The progress of this invention is related in the same manner by Schreiber, in his Life of Ruysch.

When the method of producing these skeletons became publicly known, they were soon prepared by others; some of whom made observations, which were contrary to those of Ruysch. Among these in particular were J. Bapt. Du Hamel, who, so early as the year 1727, described and illustrated with elegant engravings the interior construction of a pear 483 Trew 484 , in whose possession Keysler saw such skeletons in 1730; P. H. G. Mohring 485 ;Seba 486 ; Francis Nicholls 487 , an Englishman; Professor Hollmann 488  at Göttingen, Ludwig 489 Walther 490 ,Gesner 491  and others. Nicholls seems to have been the first who split the net of an apple- or a pear-tree leaf into two equal parts, though Ruysch split a leaf of the opuntia into three, four, and even five layers, as he himself says.

In the year 1748, Seligmann, an engraver, began to publish, in folio plates, figures of several leaves which he had reduced to skeletons 492. As he thought it impossible to make drawings sufficiently correct, he took impressions from the leaves or nets themselves, with red ink, and in a manner which may be seen described in various books on the arts. Of the greater part he gave two figures, one of the upper and another of the under side. He promised also to give figures of the objects as magnified by a solar microscope; and two plates were to be delivered monthly. Seligmann however died soon after, if I am not mistaken; and a lawsuit took place between his heirs, by which the whole of the copies printed were arrested, and for this reason the work was never completed, and is to be found only in a very few libraries.

Cobres says that eight pages of text, with two black and twenty-nine red copper-plates, were completed. The copy which is in the library of our university has only eight pages of text, consisting partly of a preface by C. Trew, and partly of an account of the author, printed in Latin and German opposite to each other. Trew gives a history of the physiology of plants and of leaf-skeletons; and Seligmann treats on the methods of preparing the latter. The number of the plates however is greater than that assigned by Cobres. The copy which is now before me contains thirty-three plates, printed in red; and besides these, two plates in black, with figures of the objects magnified. Of the second plate in red, there is a duplicate with this title, “Leaves of a bergamot pear-tree, the fruit of which is mild;” but the figures in both are not the same; and it appears that the author considered one of the plates as defective, and therefore gave another. The leaves represented in the plates are those of the orange-tree, lemon-tree, shaddock-tree, butcher's-broom, walnut-tree, pear-tree, laurel, lime-tree, ivy, medlar, chestnut-tree, maple-tree, holly, willow, white hawthorn, &c.

I shall take this opportunity of inserting here the history of the art of raising trees from leaves. The first who made this art known was Agostino Mandirola, doctor of theology, an Italian minorite of the Franciscan order. In a small work upon Gardening, which, as I think, was printed for the first time at Vicenza, in duodecimo, in the year 1652, and which was reprinted afterwards in various places, he gave an account of his having produced trees from the leaves of the cedar- and lemon-tree 493 ; but he does not relate this circumstance as if he considered it to be a great discovery. On the contrary, he appears rather to think it a matter of very little importance. His book was soon translated into German; and his account copied by other writers, such as Böckler 494  and Hohberg 495 , who were at that time much read. A gardener of Augsburg, as we are told by Agricola, was the first who imitated this experiment, and proved the possibility of it to others. He is said to have tried it with good success in the garden of count de Wratislau, ambassador at Ratisbon from the elector of Bohemia.

But never was this experiment so often and so successfully repeated as in the garden of baron de Munchhausen, at Swobber. A young tree was obtained there from a leaf of the Limon a Rivo, which produced fruit the second year. It was sent to M. Volkamer, at Nuremberg, who caused a drawing to be made from it, which was afterwards engraved, in order that it might be published in the third volume of his Hesperides; but as the author died too early, it was not printed. The exact drawing, as it was then executed at Nuremberg, and an account of the whole process employed in the experiment at Swobber, have been published by the baron de Munchhausen himself, from authentic papers in his grandfather's own writing 496.

No one, however, excited so much attention to this circumstance as the well-known George Andrew Agricola, physician at Ratisbon, who, with that confidence and prolixity which were peculiar to him, ventured to assert that trees could be propagated in the speediest manner by planting the leaves, after being steeped in a liquor which he had invented; and for the truth of his assertion he referred to his own experiments 497. Among the naturalists of that period none took more trouble to examine the possibility of this effect than Thummig 498 , who endeavoured to prove that not only leaves with eyes left to them, could, in well-moistened earth, throw out roots which would produce a stem, but that leaves also without eyes would grow up to be trees. Baron Munchhausen, on the other hand, assures us, that according to the many experiments made in his garden, one can only expect young plants from the leaves of those trees which do not bring forth buds; that experiments made with the leaves of the lemon-tree had alone succeeded, but never those made with the leaves of the orange- or lime-tree; and that Agricola and Thummig had erroneously imagined that the leaves themselves shot up into trees, their middle fibre (rachis ) becoming the stem, and the collateral fibres the branches. But the leaf decays as soon as it has resigned all its sap to the young tree, which is springing up below it.

To conclude: It is probable that the well-known multiplication of the Indian fig, or Opuntia, gave the first idea of this experiment; for every joint of that plant, stuck into the earth, and properly nurtured, throws out roots and grows. As these joints were commonly considered to be leaves, people tried whether other leaves would not grow in the like manner. Luckily, those of the lemon-tree were chosen for this purpose; and what was expected took place. Thus from a false hypothesis have new truths often been derived; and thus was Kepler, by a false and even improbable opinion, led to an assertion, afterwards confirmed, that the periodical revolutions of the planets were in proportion to their distance from the sun. But the raising of trees from leaves was too rashly declared to be a method that might be generally employed; for it is certain that it now seldom succeeds.

[Beckmann certainly overrates the value of these plant-skeletons in assisting the acquirement of a knowledge of the anatomy of plants. By macerating plants in water, all but the woody fibres are decomposed by the putrefactive fermentation which ensues. From an examination of these, a knowledge of structure merely is attainable, which may be now truly said to be thoroughly understood. It gives us no insight into its functions. The modern microscope has revealed to us the structure of all the components of vegetable tissues, and has most materially assisted in developing the functions of several; many, however, remain in the hands of the physiologist. Nevertheless, these plant-skeletons exhibit the true course and arrangement of the woody fibres, and form most beautiful objects. The leaves are not the only parts which can be thus prepared; the petals of many plants are even more delicate and beautiful in their ligneous structure, as evidenced in the hydrangea and several others. Their preparation is exceedingly simple, but tedious, and can only be well effected by maceration in water, which frequently requires to be considerably prolonged. The pulpy half-decomposed portions are gradually removed by a camel-hair pencil, or other means, with great delicacy and care; they are finally washed and bleached, if necessary, with chloride of lime or soda. By washing in considerably diluted muriatic acid and water, all traces of this reagent are removed; they are then dried, and will keep for an indefinite period.]

Footnotes

477  Museum Wormianum. Lugd. Bat. 1655, fol. p. 149.

478  The well-known Sir John Hill, an Englishman, has proved, however, in later times, the possibility of injecting a substance into the vessels of plants also. He dissolved sugar of lead in water, suspended in it bits of the finest wood, so that one-half of them was under water and the other above it, and covered the vessel in which they were placed with an inverted glass. At the end of two days he took the bits of wood out, cut off the parts which had been immersed in the water, dipped them in a warm lye made of unslaked lime and orpiment, like what was used formerly for proving wine; and by these means the finest vessels, which had been before filled with sugar of lead, acquired a dark colour, and their apertures became much more distinct. This process he describes himself in his work on the Construction of Timber.

479  Rariora Naturæ et Artis. Breslau and Leipsic, 1737, fol. p. 421.

480  Adversariorum decas iii. in Ruyschii Opera Omnia Anat. Med.

481  A. Vateri Epist. ad Ruyschium de Musculo Orbiculari, 1727. Of employing different kinds of insects, particularly the dermestes, as they are called, for reducing animal and vegetable bodies to skeletons, Hebenstreit has treated in Program. de Vermibus Anatomicorum administris. Lips. 1741. Figures of the insects and of some of their preparations are added.

482  Acta Eruditorum, 1729, Febr. p. 63.

483  Mémoires de l'Acad. des Sciences, ann. 1730, 1731, 1732.

484  Commerc. Litter. Norim. 1732, p. 73.

485  Ib.

486  Phil. Transact. 1730, ccccxvi. p. 441.

487  Ib. ccccxiv. p. 371.

488  Ib. cccclxi. p. 789, and cccclxiii. p. 796.—Commerc. Litter. Norimb. 1735, p. 353.

489  Institutiones Regni Vegetabil. In the part on Leaves.

490  Programma de Plantarum Structura. Lips. 1740, 4to, § 5, 6.

491  Dissertat. Phys. de Vegetabilibus, printed with Linnæi Orat. de Necessitate Peregrinat. intra Patriam. Lugd. B. 1743.

492  Die Nahrungs-Gefässe in den Blättern der Bäume. Nurnb. 1748.

493  Many editions of this book may be found mentioned in Halleri Bibl. Botan. i. p. 484; Böhmeri Bibl. Hist. Nat. iii. p. 679.

494  Haus- und Feld-Schule, i. 26.

495  Georgica Curiosa, i. p. 787.

496  Hausvater, vol. v. p. 662.

497  Versuch der Universal-vermehrung aller Bäume. Regensb. 1716, fol., or the edition by Brauser. Regensb. 1772.

498  Thummigii Meletemata. Brunsw. 1727, 8vo, p. 5.