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be assigned. Where Linnaeus had spoken of a class plant or generic plant, the expression 'plan of symmetry' or 'type' was used, meaning an ideal original form, from which numerous related forms might be derived. It was left undecided, whether this ideal form ever really existed, or whether it was merely the result of intellectual abstraction; and thus the forms of thought of the old philosophy soon began to reappear. The Platonic ideas, though mere abstractions and therefore only products of the understanding, had been regarded not only by the school of Plato, but also by the so-called Realists among the schoolmen, as really existing things. The systematists obtained the idea of a type by abstraction, and the next step was easy, to ascribe with the Platonists an objective existence to this creature of thought, and to conceive of the type in the sense of a Platonic idea. This was the only view that was possible in combination with the dogma of the constancy of species, and so Elias Fries, in his 'Corpus Florarum,' 1835, in speaking of the natural system, could consistently say, 'est quoddam supranaturale,' and maintain that each division of it 'ideam quandam exponit.' So long as the constancy of species is maintained, there is no escaping from the conclusion drawn by Fries, but it is equally certain that systematic botany at the same time ceases to be a scientific account of nature. Systematists, adopting this conclusion as necessarily following from the dogma, might consider themselves as seeking to express in the natural system the plan of creation, the thought of the Creator himself; but in this way systematic botany became mixed up with theological notions, and it is easy to understand why the first feeble attempts at a theory of descent encountered such obstinate, nay, fanatical opposition from professed systematists, who looked upon the system as something above nature, a component part of their religion. And if we look back we find that these views are based on the dogma of the constancy of species, while Linnaeus' 'Philosophia Botanica' teaches us on what grounds this dogma rests, where it says, 'Novas species