that the members of each of these whorls are in their nature identical, and the same as if they were whorls of ordinary leaves, brought together by the shortening their common axis, and modified in form by the successive elaboration of their nutriment. Further, according to this view, a whorl of leaves itself is to be considered as identical with several detached leaves dispersed spirally along the axis, and brought together because the axis is shortened. Thus all the parts of a plant are, or at least represent, the successive metamorphoses of the same elementary member. The root-leaves thus pass into the common leaves;—these into bractea;-these into the sepals;—these into the petals; these into the stamens with their anthers;-these into the ovaries with their styles and stigmas;—these ultimately become the fruit; and thus we are finally led to the seed of a new plant. Moreover the same notion of metamorphosis may be applied to explain the existence of flowers which are not symmetrical like those we have just referred to, but which have an irregular corolla or calyx. The papilionaceous flower of the pea tribe, which is so markedly irregular, may be deduced by easy gradations from the regular flower, (through the mimosea,) by expanding one petal, joining one or two others, and modifying the form of the intermediate ones. Without attempting to go into detail respecting the proofs of that identity of all the different organs, and all the different forms of plants, which is thus asserted, we may observe, that it rests on such grounds as these;―the transformations which the parts of flowers undergo by accidents of nutriment or exposure. Such changes, considered as monstrosities where they are very remarkable, show the tendencies and possibilities belonging to the organization in which they occur. For instance, the single wild-rose, by culture, transforms many of its numerous stamens into petals, and thus acquires the deeply folded flower of the double garden-rose. We cannot doubt of the reality of this change, for we often see stamens in which it is incomplete. In other cases we find petals becoming leaves, and a branch growing out of the centre of the flower. Some pear-trees, when in blossom, are remarkable for their tendencies to such monstrosities. Again, we find that flowers which are usually irregular, occasionally become regular, and conversely. The common snap-dragon (Linaria vulgaris) affords a curious instance of this. The usual form of this plant is "personate," the corolla being divided into two lobes, which differ in form, and 'Lindley, Nat. Syst. p. 84. Henslow, Principles of Botany, p. 116. together present somewhat the appearance of an animal's face; and the upper portion of the corolla is prolonged backwards into a tubelike "spur." No flower can be more irregular; but there is a singular variety of this plant, termed Peloria, in which the corolla is strictly symmetrical, consisting of a conical tube, narrowed in front, elongated behind into five equal spurs, and containing five stamens of equal length, instead of the two unequal pairs of the didynamous Linaria. These and the like appearances show that there is in nature a capacity for, and tendency to, such changes as the doctrine of metamorphosis asserts. Göthe's Metamorphosis of Plants was published 1790: and his system was the result of his own independent course of thought. The view which it involved was not, however, absolutely new, though it had never before been unfolded in so distinct and persuasive a manner. Linnæus considered the leaves, calyx, corolla, stamens, each as evolved in succession from the other; and spoke of it as prolepsis or anticipa tion," when the leaves changed accidentally into bracteæ, these into a calyx, this into a corolla, the corolla into stamens, or these into the pistil. And Caspar Wolf apprehended in a more general manner the same principle. "In the whole plant," says he, "we see nothing but leaves and stalk;" and in order to prove what is the situation of the leaves in all their later forms, he adduces the cotyledons as the first leaves. 6 Göthe was led to his system on this subject by his general views of nature. He saw, he says, that a whole life of talent and labor was requisite to enable any one to arrange the infinitely copious organic forms of a single kingdom of nature. "Yet I felt," he adds, "that for me there must be another way, analogous to the rest of my habits. The appearance of the changes, round and round, of organic creatures had taken strong hold on my mind. Imagination and Nature appeared to me to vie with each other which could go on most boldly yet most consistently." His observation of nature, directed by such a thought, led him to the doctrine of the metamorphosis. In a later republication of his work (Zur Morphologie, 1817,) he gives a very agreeable account of the various circumstances which affected the reception and progress of his doctrine. Willdenow' quoted 5 Sprengel, Bot. ii. 302. Amæn. Acad. vi. 324, 365. Nov. Con. Ac. Petrop. xii. 403, xiii. 478. Zur Morph. i. 30. Zur Morph. i. 121. him thus:-"The life of plants is, as Mr. Göthe very prettily says, an expansion and contraction, and these alternations make the various periods of life." "This 'prettily," says Göthe, "I can be well content with, but the egregie' of Usteri is much more pretty and obliging." Usteri had used this term respecting Göthe in an edition of Jussieu. The application of the notion of metamorphosis to the explanation of double and monstrous flowers had been made previously by Jussieu. Göthe's merit was, to have referred to it the regular formation of the flower. And as Sprengel justly says,' his view had so profound a meaning, made so strong an appeal by its simplicity, and was so fruitful in the most valuable consequences, that it was not to be wondered at if it occasioned further examination of the subject; although many persons pretend to slight it. The task of confirming and verifying the doctrine by a general application of it to all cases,-a labor so important and necessary after the promulgation of any great principle,Göthe himself did not execute. At first he collected specimens and made drawings with some such view, but he was interrupted and diverted to other matters. "And now," says he, in his later publication, "when I look back on this undertaking, it is easy to see that the object which I had before my eyes was, for me, in my position, with my habits and mode of thinking, unattainable. For it was no less than this: that I was to take that which I had stated in general, and presented to the conception, to the mental intuition, in words; and that I should, in a particularly visible, orderly, and gradual manner, present it to the eye; so as to show to the outward sense that out of the germ of this idea might grow a tree of physiology fit to overshadow the world." 10 Voigt, professor at Jena, was one of the first who adopted Göthe's view into an elementary work, which he did in 1808. Other botanists labored in the direction which had thus been pointed out. Of those who have thus contributed to the establishment and developement of the metamorphic doctrine, Professor De Candolle, of Geneva, is perhaps the most important. His Theory of Developement rests upon two main principles, abortion and adhesion. By considering some parts as degenerated or absent through the abortion of the buds. which might have formed them, and other parts as adhering together, he holds that all plants may be reduced to perfect symmetry: and the actual and constant occurrence of such incidents is shown beyond • Gesch. Botan. ii. 304. 1 Zur Morph. i. 229. all doubt. And thus the snap-dragon, of which we have spoken above, is derived from the Peloria, which is the normal condition of the flower, by the abortion of one stamen, and the degeneration of two others. Such examples are too numerous to need to be dwelt on. Sect. 2.-Application of Vegetable Morphology. THE doctrine, being thus fully established, has been applied to solve different problems in botany; for instance, to explain the structure of flowers which appear at first sight to deviate widely from the usual forms of the vegetable world. We have an instance of such an application in Mr. Robert Brown's explanation of the real structure of various plants which had been entirely misunderstood: as, for example, the genus Euphorbia. In this plant he showed that what had been held to be a jointed filament, was a pedicel with a filament above it, the intermediate corolla having evanesced. In Orchidea (the orchis tribe), he showed that the peculiar structure of the plant arose from its having six stamens (two sets of three each), of which five are usually abortive. In Conifera (the cone-bearing trees), it was made to appear that the seed was naked, while the accompanying appendage, corresponding to a seed-vessel, assumed all forms, from a complete leaf to a mere scale. In like manner it was proved that the pappus, or down of composite plants (as thistles), is a transformed calyx. Along with this successful application of a profound principle, it was natural that other botanists should make similar attempts. Thus Mr. Lindley was led to take a view" of the structure of Reseda (mignonette) different from that usually entertained; which, when published, attracted a good deal of attention, and gained some converts among the botanists of Germany and France. But in 1833, Mr. Lindley says, with great candor, "Lately, Professor Henslow has satisfactorily proved, in part by the aid of a monstrosity in the common Mignonette, in part by a severe application of morphological rules. that my hypothesis must necessarily be false." Such an agreement of different botanists respecting the consequences of morphological rules, proves the reality and universality of the rules. We find, therefore, that a principle which we may call the Principle of Developed and Metamorphosed Symmetry, is firmly established " Lindley, Brit. Assoc. Report, iii. 50. and recognized, and familiarly and successfully applied by botanists. And it will be apparent, on reflection, that though symmetry is a notion which applies to inorganic as well as to organic things, and is, in fact, a conception of certain relations of space and position, such developement and metamorphosis as are here spoken of, are ideas entirely different from any of those to which the physical sciences have led us in our previous survey; and are, in short, genuine organical or physiological ideas;-real elements of the philosophy of life. We must, however imperfectly, endeavor to trace the application of this idea in the other great department of the world of life; we must follow the history of Animal Morphology. THE CHAPTER VII. PROGRESS OF ANIMAL MORPHOLOGY. Sect. 1.-Rise of Comparative Anatomy. HE most general and constant relations of the form of the organs, both in plants and animals, are the most natural grounds of classification. Hence the first scientific classifications of animals are the first steps in animal morphology. At first, a zoology was constructed by arranging animals, as plants were at first arranged, according to their external parts. But in the course of the researches of the anatomists of the seventeenth century, it was seen that the internal structure of animals offered resemblances and transitions of a far more coherent and philosophical kind, and the Science of Comparative Anatomy rose into favor and importance. Among the main cultivators of this science' at the period just mentioned, we find Francis Redi, of Arezzo; Guichard-Joseph Duvernay, who was for sixty years Professor of Anatomy at the Jardin du Roi at Paris, and during this lapse of time had for his pupils almost all the greatest anatomists of the greater part of the eighteenth century; Nehemiah Grew, secretary to the Royal Society of London, whose Anatomy of Plants we have already noticed. But Comparative Anatomy, which had been cultivated with ardor 1 Cuv. Leçons sur l'Hist. des Sc. Nat. 414, 420. |