Since these several varieties are only one degree removed from each other, M. De Candolle supposes divergence to be the natural law which has governed their growth, and not hereditary fixity. But here again he has only remote probabilities to work upon, no absolute data. We are still speaking of his fossilized herbaria, not his modern specimens. These may show a large number of genetically-connected individuals, or those claimed to be so connected. And yet no naturalist can be certain that, because they exhibit similarly marked characteristics, the one ever descended from the other; for the universal experience-rule still holds good that "like engenders like," and we search in vain for anything more than a similarity of _idea_, or logical connection, which justifies a recognition of the _individuorum similium_ in Jessieu's definition of species. But similarity must not be mistaken for absolute likeness, which nowhere exists in nature. Infinite diversity is the law, absolute identity the rarest possible exception. No two oak leaves, for instance, in a million will be found actually alike, although taken from the same tree, or trees of the same variety; and the same may be said of the segmentation and branching of their limbs, as well as the striatures of their corticated covering, _Et sic de similibus_ everywhere, and with respect to every thing. Nature is more solicitous of diversity and beauty, than of similarity and tameness of effect, in all her landscape pictures; and the Platonic conception that "contraries spring from contraries," may be only a supplementary truth to that of _de similibus_. In the eye of the soul all objective existences are discerned in their logical order, or as consecutive thoughts of the Divine mind, as outspoken in the material universe. To insist upon cutting down these transcendental forms[20] into the smallest possible number of similar or identical forms, may be all well enough to accomplish scientific classification; but the productive power of nature can never be limited by these mental processes of our own.