« 이전계속 »
two hundred and forty years since Caspar Bauhin, in his Pinas, attempted to collect in one work, all the plants which had been described by all preceding botanists, and to present, embodied as it were in one tablet, a representation of the vegetable kingdom. This effort was not only laborious, it remained incomplete after forty years of assiduous toil) but from the insufficient modes and systems under which plants had been described, and the consequent uncertainty in which they were still involved, was altogether unsatisfactory. The same causes obstructed every similar attempt that was made, before some uniform plan of describing plants had been adopted. The first successful effort, after botany may be considered as a science, to describe in one work the plants of all countries, was, as we have already noticed, the “Species Plantarum” of Linnæus, published in 1753_maximum opus et eternum, as it was well styled by Haller. A second edition was published in 1762, each of these was in two volumes. In subsequent editions, it was, of necessity, greatly enlarged. Willdenow commenced his celebrated edition in 1797, and, at his death, had completed ten parts or volumes, extending to the ferns, inclusively. The remaining orders of the cryptogamic plants have never been published. The prodigious accessions which have been made to botany, since the commencement of the present century-accessions which became conspicuously manifest in the concluding volumes of Willdenow, appeared to deter persons for some time from encountering the immense labour which a new edition, however much called for, would require. At length Roemer and Schultes commenced this task, and their edition of the “Species Plantarum,” though, perhaps, somewhat retarded by the death of one of the associates, is still in progress. In the meantime, those who had adopted the system of Jussieu, had done nothing but publish monographs of particular orders, or had applied the system to the Flora of one or two countries, until at length, the great enterprize of combining in their proper orders, all the plants which had been discovered, and whose numbers were daily augmenting, was undertaken by the author of the work before us.
No man in Europe could have come better prepared to this arduous undertaking. The life of M. De Candolle has been devoted to the study of botany. He was distinguished among the eminent men of France for his sagacity, perseverance and attainments. Besides many dissertations on subjects connected with this science, and on different genera and families of plants, he had published as a preparatory exercise, a “Flore Française,” which has passed through several editions. He was for some time Professor of Botany at Montpellier, and when exiled from France,
on the restoration of the Bourbons, he returned to Geneva, his
On the fundamental principles of his classification, we think
" I will explain here in few words the characters of these great classes, and the series of families of which they are composed.
“Let us consider at first the whole vegetable kingdom, and endeavour to apply the principles we have already stated, to divide it into general classes, either according to the functions of nutrition or those of reproduction.
VOL. IV.-NO 8.
“As to the organs of nutrition, I select the most important of all, to wit, the vessels, and I consider them under that point of view which is the most essential of all--their presence or their absence. It is evident, in fact, that the anatomical circumstances wbich influence nutrition most powerfully, are the existence or non-existence of vesselsof those organs which seem at first view so essential, that it is difficult to form an idea of the life of a being that is deprived of them. On this principle then, we will divide vegetables into two classes--vascular and cellular. This division appears to be connected with every thing most remarkable that the nutritive organs present. Thus, with the existence of vessels are found constantly united, 1st, the existence of stomata or cortical pores ; 2ndly, the evident distinction between the roots and the stem, consequently, the existence of a collum. The absence of vessels, on the other hand, announces, 1st, the absence of cortical pores; and 2ndly, the impossibility of distinguishing with precision the root from the stem. But to assure ourselves whether this division is really natural, it is necessary to recur to an examination of the organs of reproduction. Here let us ask, what is the first of these organs? Undoubtedly, the embryo, and the most important point in which it can be considered, is its absence or presence.
Here then, with M. Richard, we might, in the first place, distinguish all plants into those with, and those without an embryo. But as we have no proof that any organized beings really exist without an embryo, and as it is impossible to establish the basis of a classification upon a question of fact which cannot be solved by our senses, let us change the question into the following :-admitting that there exists in all vegetables a germ or reproductive corpuscle, what part of that corpuscle is the most essential. It can be neither the radicle nor the plumula, which, by the hypothesis itself, is common to all plants; it must be then the cotyledons, that is, the special organ with which the reproductive corpuscle is furnished for its developement. We will then state that in the function of reproduction, that which is most essential, is to know whether the embryos have or have not cotyledons, and will divide vegetables into two classes, cotyledonous and acotyledonous. This idea is strengthened when we perceive that all the plants that are classed among the acotyledonous, are the same that many authors sup pose to be destitute of an embryo. And it is remarkable, that by the two methods, we arrive at the same results; thus the vascular vegetables are the saine as those with cotyledons, and the cellular vegetables the same as those without cotyledons; and this division is natural.
“Let us now take the vascular or cotyledonous vegetables, and apply to them the same train of reasoning.
“ As to the organs of nutrition, we will take the first of these organs, to wit, the vessels, and consider them no longer in the first point of view, as that has been already employed for the primitive division, but in a second, that is, their position, and establish their classification upon the position of the vessels. In this view it may be perceived, that there are vascular vegetables, where the vessels are all sensibly concentric around a cellular pith or cell, and arranged in such a manner that the oldest are in the centre, and the youngest at the circumference, whence it follows that the plant hardens from within to without. These we have distinguished by the name of Exogene, liw-yévñw.) We may perceive, on the other hand, that there are other vegetables in which the vessels are scattered through all the stem, not ranged in zones around a central point, and disposed in such a manner that the oldest, that is to say, the hardest are at the surface, and the principal growth of the stem takes place within. From this peculiarity, is derived the name of Endogenæ, which we have imposed on this class. Besides the fundamental characters that we have just indicated, let us add that the Exogenæ have a canal and medullary rays of which the Endogenæ are destitute; that the first have a form necessarily more or less conic, whilst that of the second is really cylindric: that the age of the first is known by the number of concentric layers, whilst that of the second is measured by the number of rings more or less visible on the stem, when examined in a vertical direction. Let us add, the nerves of the leaves are generally branching in the exogenous, simple in the endogenous plants, that the leaves themselves are rarely sheathing in the first class, very frequently in the second.
" Let us now consider the same vascular plants, as regards the organs of their reproduction. Let us select the most essential of these organs, to wit, the cotyledons, and consider them, not according to their number, as we have done before, but according to their position, which, as we have stated, is the most important of its characters, except that of its existence. Now we will perceive that in this respect, vegetables are divided into two great classes, namely, those in which the cotyledons are opposite or verticillate; these, to conform to common usage, we will call dicotyledonous, and those in which the cotyledons are alternate, which we will call on the same principle, monocotyledonous plants. As these cotyledons are in reality oniy the first leaves present in the seed, just as the radicle is but the root, and the plumula the stalk, it follows, from this disposition of the cotyledons, 1st. That the Dycotyledoneæ must bave their primordial leaves opposite or verticillate, which may, however, become alternate by the act of vegetation ; that the Monocotyledoneæ, on the contrary, have the primordial leaves alternate, but which, in turn, may become verticillate or (more rarely) opposite. 2ndly. That the number of cotyledons is not fixed; in the dicotyledonous plants, it may vary from two, which is the most common number, to three, four, five and upwards; in the monocotyledonous it may vary from one, the usual number, to two as in the Cycas, which is, nevertheless, not a dycotyledonous plant, to three, as in certain grasses, &c. The number depends solely on the number of leaves already developed and visible in the seed.
“Now, if we compare the division of the vascular plants, with reference to their organs of nutrition or reproduction, we will find that the exogenous plants are exactly the same as the dicotyledonous, and the endogenous exactly the same as the monocotyledonous. This division then is also natural.-Theorie Elémentaire, foc. Paris, 1819. pp. 237, 242.
Even from this able exposition it is apparent, that however great has been the improvement which this system has made in the arrangement of plants, its own fundamental principles are
liable to some objections, and weakened by the uncertainty wbich hangs about them. The number of cotyledons apparently the very basis of the system is not invariable,* while the habit as arising from foliation is still more mutable. A wide field remains open to encourage and reward the labour of botanists; and this science has perhaps yet to receive its most important modifications.
M. De Candolle is one of those who have undertaken to remodel the system of Jussieu, so far at least as the arrangement of the orders is concerned. His reasons for this alteration, he has stated in his “Theorie Elémentaire,” which he considered as the preface to his “Systema Naturale," and if not so important as the doctrines he has just been examining, they, nevertheless, are worthy of our attention. After noticing that the vegetable kingdom resembles a geographical chart, much more than a continued chain of being, because as he afterwards observes “each genus, each family does not only resemble the groups which immediately precede and follow, but has multiplied relations with many others. The linear order cannot shew us these relations, and yet it is the knowledge of them which constitutes, really, the difference between one classifier and another:" he continues
“ All that I have been considering proves evidently, in my opinion, that there does not exist in nature any continued series ; that beings are grouped together at distances very unequal, and, that it is impossible to express their true relations in a linear order. But, nevertheless, for the accustomed form of our treatises, even for instruction and the arrangement of collections, it is necessary to adopt a series, understanding at the same time, that it is only adopted for convenience, and is truly artificial, at least, in its details. The classes alone may be arranged in a natural order, according to the degree of their complexity; and in this view two methods may be pursued; one to ascend from the most simple to the most compound as M. Jussieu has done, or to descend from the compound to the simple, as the Zoologists do, and as Haller and La Marck have done in the vegetable kingdom. The question in itself, is of little importance, but it is, nevertheless, necessary to consider it for a moment.
“At the first view, nothing appears more philosophical, that to commence a series by the most simple beings, and to ascend by degrees to those whose structure is more complex. This course appears the more adapted to the vegetable kingdom, because we know or believe that we know more certainly which are the most simple vegetables, than which are the most complex.
“ But if we examine the question more attentively, above all, if we refer to experience, we find many inconveniences in commencing by the most simple vegetables. The most simple beings of each kingdom are the least perfectly known, and it is contrary to all the rules of logic
* Invariable, perhaps, in the genus, but not in the class.