It was not till the younger Jussieu had employed himself for nineteen years upon botany, that he published, in 1789, his Genera Plantarum; and by this time he had so entirely formed his scheme in his head, that he began the impression without having written the book, and the manuscript was never more than two pages in advance of the printer’s type.
When this work appeared, it was not received with any enthusiasm; indeed, at that time, the revolution of states absorbed the thoughts of all Europe, and left men little leisure to attend to the revolutions of science. The author himself was drawn into the vortex of public affairs, and for some years forgot his book. The method made its way slowly and with difficulty: it was a long time before it was comprehended and adopted in France, although the botanists of that country had, a little while before, been so eager in pursuit of a natural system. In England and Germany, which had readily received the Linnæan method, its progress was still more tardy.
There is only one point, on which it appears necessary further to dwell. A main and fundamental distinction in all natural systems, is that of the Monocotyledonous and Dicotyledonous plants; that is, plants which unfold themselves from an embryo with two little leaves, or with one leaf only. This distinction produces its effects in the systems which are regulated by numbers; for the flowers and fruit of the monocotyledons are generally referrible to some law in which the number three prevails; a type which rarely occurs in dicotyledons, these affecting most commonly an arrangement founded on the number five. But it appears, when we attempt to rise towards a natural [408] method, that this division according to the cotyledons is of a higher order than the other divisions according to number; and corresponds to a distinction in the general structure and organization of the plant. The apprehension of the due rank of this distinction has gradually grown clearer. Cuvier[117] conceives that he finds such a division clearly marked in Lobel, in 1581, and employed by Ray as the basis of his classification a century later. This difference has had its due place assigned it in more recent systems of arrangement; but it is only later still that its full import has been distinctly brought into view. Desfontaines discovered[118] that the ligneous fibre is developed in an opposite manner in vegetables with one and with two cotyledons;—towards the inside in the former case, and towards the outside in the latter; and hence these two great classes have been since termed endogenous and exogenous. ~Additional material in the [3rd edition].~
[117] Hist. Sc. Nat. ii. 197.
[118] Hist. Sc. Nat. i. pp. 196, 290.
Thus this division, according to the cotyledons, appears to have the stamp of reality put upon it, by acquiring a physiological meaning. Yet we are not allowed to forget, even at this elevated point of generalization, that no one character can be imperative in a natural method. Lamarck, who employed his great talents on botany, before he devoted himself exclusively to other branches of natural history, published his views concerning methods, systems,[119] and characters. His main principle is, that no single part of a plant, however essential, can be an absolute rule for classification; and hence he blames the Jussieuian method, as giving this inadmissible authority to the cotyledons. Roscoe[120] further urges that some plants, as Orchis morio, and Limodorum verecundum, have no visible cotyledons. Yet De Candolle, who labored along with Lamarck, in the new edition of the Flore Française, has, as we have already intimated, been led, by the most careful application of the wisest principles, to a system of Natural Orders, of which Jussieu’s may be looked upon as the basis; and we shall find the greatest botanists, up to the most recent period, recognizing, and employing themselves in improving, Jussieu’s Natural Families; so that in the progress of this part of our knowledge, vague and perplexing as it is, we have no exception to our general aphorism, that no real acquisition in science is ever discarded.
[119] Sprengel, ii. 296; and, there quoted, Flore Française, t. i. 3, 1778. Mém. Ac. P. 1785. Journ. Hist. Nat. t. i. For Lamarck’s Méthode Analytique, see Dumeril, Sc. Nat. i. Art. 390.
[120] Roscoe, Linn. Tr. vol. xi. Cuscuta also has no cotyledons.
[409] The reception of the system of Jussieu in this country was not so ready and cordial as that of Linnæus. As we have already noticed, the two systems were looked upon as rivals. Thus Roscoe, in 1810,[121] endeavored to show that Jussieu’s system was not more natural than the Linnæan, and was inferior as an artificial system: but he argues his points as if Jussieu’s characters were the grounds of his distribution; which, as we have said, is to mistake the construction of a natural system. In 1803, Salisbury[122] had already assailed the machinery of the system, maintaining that there are no cases of perigynous stamens, as Jussieu assumes; but this he urges with great expressions of respect for the author of the method. And the more profound botanists of England soon showed that they could appreciate and extend the natural method. Robert Brown, who had accompanied Captain Flinders to New Holland in 1801, and who, after examining that country, brought home, in 1805, nearly four thousand species of plants, was the most distinguished example of this. In his preface to the Prodromus Floræ Novæ Hollandiæ, he says, that he found himself under the necessity of employing the natural method, as the only way of avoiding serious error, when he had to deal with so many new genera as occur in New Holland; and that he has, therefore, followed the method of Jussieu; the greater part of whose orders are truly natural, “although their arrangement in classes, as is,” he says, “conceded by their author, no less candid than learned, is often artificial, and, as appears to me, rests on doubtful grounds.”
[121] Linn. Tr. vol. xi. p. 50.