In pursuing these reflections, which have the conception of species chiefly in view, he arrives at the following proposition: That according to the law of nature like always produces like, and that which is of the same species with itself.
All that Cesalpino says on systematic arrangement shows that he was perfectly clear in his own mind with regard to the distinction between a division on subjective grounds, and one that respects the inner nature of plants themselves, and that he accepted the latter as the only true one. He says, for instance, in the next chapter: ‘We seek out similarities and dissimilarities of form, in which the essence (‘substantia’) of plants consists, but not of things which are merely accidents of them (‘quae accidunt ipsis’).’ Medicinal virtues and other useful qualities are, he says, just such accidents. Here we see the path opened, along which all scientific arrangement must proceed, if it is to exhibit real natural affinities; but at the same time there is a warning already of the error which beset systematic botany up to Darwin’s time; if in the above sentence we substitute the word idea for that of substance, and the two expressions have much the same meaning in the Aristotelian and Platonic view of nature, we recognise the modern predarwinian doctrine, that species, genera, and families represent ‘ideam quandam’ and ‘quoddam supranaturale.’
Pursuing his deductions, Cesalpino next shows, that the most important divisions, those of woody plants and herbs, must be maintained in accordance with the most important function of vegetation, that of drawing up the food through root and shoot; this division passed from the first and later on up to the time of Jung for an unassailable dogma, to which science simply had to conform. The second great function of plants is the producing their like, and this is effected by the parts of fructification. Though these parts are only found in the more perfect forms, yet the subdivisions (‘posteriora genera’) must be derived in both trees and herbs from likeness and unlikeness in the fructification. And thus Cesalpino was led, not by induction but by the deductive path of pure Aristotelian philosophy, to the conclusion, that the principles of a natural classification are to be drawn from the organs of fructification; for which conclusion Linnaeus declared him to be the first of systematists, while he thought de l’Obel and Kaspar Bauhin, who founded their arrangements on the habit only, scarcely deserving of notice.
It appears, then, that Cesalpino obtained the subdivisions which he founded on the organs of fructification from a priori views of the comparative value of organs, such as run through all Aristotelian philosophy. Of much interesting matter in the remainder of his introduction we must mention only that he makes the highest product of plants to be the fructification, of animals sense and movement, of man the intellect; and because the latter stands in need of no special bodily instruments, there is no specific difference in men, and therefore only one species of man.
In his 14th chapter he gives in broad outline a view of the system of plants which he founded on the fructification, beginning with the least perfect; no one who knows the botanical writers of the 17th and 18th centuries will be surprised to find that Cesalpino admits the doctrine of ‘generatio spontanea’ in the case of the lower plants, and in a somewhat crude form; this came from the teaching of Aristotle, and even a hundred years later Mariotte endeavoured to set up a plausible defence of spontaneous generation on physical grounds even in highly developed plants.
‘Some plants,’ says Cesalpino, ‘have no seed; these are the most imperfect, and spring from decaying substances; they have only therefore to feed themselves and grow, and are unable to produce their like; they are a sort of intermediate existences between plants and inanimate nature. In this respect Fungi resemble Zoophytes, which are intermediate between plants and animals, and of the same nature are the Lemnae, Lichenes, and many plants which grow in the sea.’
Some on the other hand produce seed, which they form after their peculiar nature in an imperfect condition, as the mule among animals; these are of the same nature as mere monstrosities or diseased growths of other plants, and many occur in the class of grain and bear empty ears. Cesalpino is evidently speaking of the Ustilagineae, but he includes also the Orobancheae and Hypocystis, which instead of seed contain only a powder; and he adds that some of the more perfect plants are sterile, but they do not belong to this division, because the peculiarity is confined in their case to individuals.
Some plants bear a substance, a kind of wool, on the leaves, which to some extent answers to seed, because it serves to propagate the plant; such plants have neither stem, flower, nor true seed, and the Ferns are of this kind. We should notice this conclusion from Cesalpino’s morphology, that plants without true seeds have also no stem; the view that ferns have no stems continued to be held by later botanists, though the original reason for it was gradually lost; and those who in the middle of the 19th century argued still in favour of this opinion, little suspected that they were endeavouring to establish a dogma of the Aristotelian philosophy. It is a similar case to that of the crown of the root mentioned above. But other plants, continues Cesalpino, produce true seeds; and he proceeds to treat of this division first, on account of its great extent as comprising all perfect plants. Three things, he says, contribute especially to the constitution of organs, the number, position, and shape of the parts; the play of nature in the composition of fruits varies according to their differences, and hence arise the different divisions of plants. He then shows how he proposes to apply these relations to the framing of his system, but his various points of view may be omitted here, as they can be better and more shortly gathered from the table below.
Other marks to be derived from roots, stems, and leaves, may be used, he says, for forming the smaller divisions. Lastly, some marks which contribute to the constitution neither of the whole plant nor of the fruit, such as colour, smell, taste, are mere accidents and are due to cultivation, place of growth, climate, and other causes.
The first of Cesalpino’s sixteen books ends with this general view of his system. The remaining fifteen books contain about 600 pages of descriptions of individual plants arranged in fifteen classes; some of the descriptions are exceedingly minute; the trees come first, and are followed by the shrubs on account of their affinity (‘ob affinitatem’). Two things have interfered with the recognition and acceptance of this system; the omission of a general view to precede the text, and its appearance in the traditional form of books and chapters, such as we find in de l’Écluse, Dodoens, and Bauhin, instead of in classes and orders, though it is true that the headings and introductions to the several books contain the designations and general characteristics of the classes described in them. Linnaeus has done good service by giving in his ‘Classes Plantarum’ a general view of all the systems proposed before his time, among which he gives the first rank to that of Cesalpino; he has also pointed out the peculiar characteristics of each system, and has appended to the old names of the genera those with which he has himself made us familiar. This invaluable work, which is a key to the understanding of the efforts that were made in systematic botany from Cesalpino to Linnaeus himself, will often be referred to in later pages of this history; it will supply us here with a tabular view of Cesalpino’s main divisions as precisely formulated by Linnaeus, which is well worth the space it will occupy, as presenting the first plan proposed for a systematic arrangement of the vegetable kingdom, with characters for each division. For the better understanding of these diagnoses it should be remembered that the ‘cor’ (heart) is the important point in the seed with Cesalpino, and that it is the place in the embryo where the radicle and the plumule unite, as has been said in a former page; Cesalpino himself says somewhat inexactly, the place from which the cotyledons spring.