But the main point of difference lies in the fact, that the system is presented by de l’Obel and Bauhin without any statement of the principles on which it rests; in their account of it the association of ideas is left to perfect itself in the mind of the reader, as it grew up before in the authors themselves. De l’Obel and Bauhin are like artists, who convey their own impressions to others not by words and descriptions, but by pictorial representations; Cesalpino, on the other hand, addresses himself at once to the understanding of his reader and shows him on philosophic grounds that there must be a classification, and states the principles of this classification; it was on philosophic grounds also that he made the characters of the seed and the fruit the basis of his arrangement, while the German botanists, paying little attention to the organs of fructification, were chiefly influenced by the general impression produced by the plant, by its habit as the phrase now is. The historians of botany have overlooked the real state of the case as here presented, or have not described it with sufficient emphasis; due attention has not been paid to the fact, that systematic botany, as it began to develope in the 17th century, contained within itself from the first two opposing elements; on the one hand the fact of a natural affinity indistinctly felt, which was brought out by the botanists of Germany and the Netherlands, and on the other the desire, to which Cesalpino first gave expression, of arriving by the path of clear perception at a classification of the vegetable kingdom which should satisfy the understanding. These two elements of systematic investigation were entirely incommensurable; it was not possible by the use of arbitrary principles of classification which satisfied the understanding to do justice at the same time to the instinctive feeling for natural affinity which would not be argued away. This incommensurability between natural affinity and _a priori_ grounds of classification is everywhere expressed in the systems embracing the whole vegetable kingdom, which were proposed up to 1736, and which including those of Cesalpino and Linnaeus were not less in number than fifteen. It is the custom to describe these systems, of which those of Cesalpino, Morison, Ray, Bachmann (Rivinus), and Tournefort are the most important, by the one word ‘artificial’[1]; but it was by no means the intention of those men to propose classifications of the vegetable kingdom which should be merely artificial, and do no more than offer an arrangement adapted for ready reference. It is true that the botanists of the 17th century and Linnaeus himself often spoke of facility of use as a great object to be kept in view in constructing a system; but every one who brought out a new system did so really because he believed that his own was a better expression of natural affinities than those of his predecessors. If some like Ray and Morison