The authors of the oldest herbals of the 16th century, Brunfels, Fuchs, Bock, Mattioli and others, regarded plants mainly as the vehicles of medicinal virtues; to them plants were the ingredients in compound medicines, and were therefore by preference termed ‘simplicia,’ simple constituents of medicaments. Their chief object was to discover the plants employed by the physicians of antiquity, the knowledge of which had been lost in later times. The corrupt texts of Theophrastus, Dioscorides, Pliny and Galen had been in many respects improved and illustrated by the critical labours of the Italian commentators of the 15th and of the early part of the 16th century; but there was one imperfection which no criticism could remove,—the highly unsatisfactory descriptions of the old authors or the entire absence of descriptions. It was moreover at first assumed that the plants described by the Greek physicians must grow wild in Germany also, and generally in the rest of Europe; each author identified a different native plant with some one mentioned by Dioscorides or Theophrastus or others, and thus there arose as early as the 16th century a confusion of nomenclature which it was scarcely possible to clear away. As compared with the efforts of the philological commentators, who knew little of plants from their own observation, a great advance was made by the first German composers of herbals, who went straight to nature, described the wild plants growing around them and had figures of them carefully executed in wood. Thus was made the first beginning of a really scientific examination of plants, though the aims pursued were not yet truly scientific, for no questions
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 were proposed as to the nature of plants, their organisation or mutual relations; the only point of interest was the knowledge of individual forms and of their medicinal virtues.
The descriptions were at first extremely inartistic and unmethodical; but the effort to make them as exact and clear as was possible led from time to time to perceptions of truth, that came unsought and lay far removed from the object originally in view. It was remarked that many of the plants which Dioscorides had described in his Materia Medica do not grow wild in Germany, France, Spain, and England, and that conversely very many plants grow in these countries, which were evidently unknown to the ancient writers; it became apparent at the same time that many plants have points of resemblance to one another, which have nothing to do with their medicinal powers or with their importance to agriculture and the arts. In the effort to promote the knowledge of plants for practical purposes by careful description of individual forms, the impression forced itself on the mind of the observer, that there are various natural groups of plants which have a distinct resemblance to one another in form and in other characteristics. It was seen that there were other natural alliances in the vegetable world, beside the three great divisions of trees, shrubs, and herbs adopted by Aristotle and Theophrastus. The first perception of natural groups is to be found in Bock, and later herbals show that the natural connection between such plants as occur together in the groups of Fungi, Mosses, Ferns, Coniferae, Umbelliferae, Compositae, Labiatae, Papilionaceae was distinctly felt, though it was by no means clearly understood how this connection was actually expressed; the fact of natural affinity presented itself unsought as an incidental and indefinite impression, to which no great value was at first attached. The recognition of these groups required no antecedent philosophic reflection or conscious attempt to classify the objects in the vegetable world; they present themselves to the unprejudiced eye as naturally as do the groups of mammals, birds, reptiles,
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 fishes and worms in the animal kingdom. The real resemblance of the organisms in such groups is unconsciously accepted by the mind through the association of ideas, and it is not till this involuntary mental act, which in itself requires no effort of the understanding, is accomplished, that any necessity is felt for obtaining a clearer idea of the phenomenon, and the sense of this necessity is the first step to intentional systematic enquiry. The series of botanical works published in Germany and the Netherlands from 1530 to 1623, from Brunfels to Kaspar Bauhin, shows very plainly how this perception of a grouping by affinity in the vegetable kingdom grew more and more distinct; but it also shows how these men merely followed an instinctive feeling in the matter, and made no enquiry into the cause of the relationship which they perceived.
Nevertheless a great step in advance was thus taken; all the foreign matter introduced into the description of plants by medical superstition and practical considerations was seen to be of secondary importance, and was indeed altogether thrown aside by Kaspar Bauhin; the fact of natural affinity, the vivifying principle of all botanical research, came to the front in its place, and awakened the desire to distinguish more exactly whatever was different, and to bring together more carefully all that was like in kind. Thus the idea of natural affinity in plants is not a discovery of any single botanist, but is a product, and to some extent an incidental product, of the practice of describing plants.
But before the exhibition of the natural affinity gave birth to the first efforts at classification on the part of de l’Obel (Lobelius) and afterwards of Kaspar Bauhin, the Italian botanist Cesalpino (1583) had already attempted a system of the vegetable kingdom on a very different plan. He was led to distribute all vegetable forms into definite groups not by the fact of natural affinity, which impressed itself on the minds of the botanists of Germany and the Netherlands through involuntary association
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 of ideas, but by philosophical reflection. Trained in the philosophy which flourished in Italy in the 16th century, deeply imbued with the doctrines of Aristotle, and practised in all subtleties of the schools, Cesalpino was not the man to surrender himself quietly to the influence of nature on the unconscious powers of the mind; on the contrary, he sought from the first to bring all that he learnt from the writings of others and from his own acute observation of the forms of plants into subjection to his own understanding. Hence he approached the task of the scientific botanist in an entirely different way from that of de l’Obel and Kaspar Bauhin. It was by philosophical reflections on the nature of the plant and on the substantial and accidental value of its parts, according to Aristotelian conceptions, that he was led to distribute the vegetable kingdom into groups and sub-groups founded on definite marks.
This difference in the origin of the systematic efforts of Cesalpino on the one hand and of de l’Obel and Bauhin on the other is unmistakably apparent; the Germans were instinctively led by the resemblances to the conception of natural groups, Cesalpino on the contrary framed his groups on the sharp distinctions which resulted from the application of predetermined marks; all the faults in Bauhin’s system are due to incorrect judgment of resemblances, those of Cesalpino to incorrectness in distinguishing.
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 classifi
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cation; 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
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 arrangement adapted for ready reference. It is true that the botanists of the 17th century and Linnaeus himself often sp............