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 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 were more influenced by the wish to exhibit natural affinities by means of a system, and others as tournefort and magnol thought more of framing a perspicuous and handy arrangement of plants, yet it is plain from the objections which every succeeding systematist makes to his predecessors, that the exhibition of natural affinities was more or less clearly in the minds of all as the main object of the system; only they all employed the same wrong means for securing this end, for they fancied that natural affinities could be brought out by the use of a few easily recognised marks, whose value for systematic purposes had been arbitrarily determined. this opposition between means and end runs through all systematic botany from cesalpino in 1583 to linnaeus in 1736.

but a new departure dates from linnaeus himself, since he was the first who clearly perceived the existence of this discord. he was the first who said distinctly, that there is a natural system of plants, which could not be established by the use of predetermined marks, as had been previously attempted, and that even the rules for framing it were still undiscovered. in his fragments of the date of 1738, he gave a list of sixty-five groups or orders, which he regarded provisionally as cycles of natural affinity, but he did not venture to give their characteristic marks. these groups, though better separated and more naturally arranged than those of kaspar bauhin, were like his founded solely on a refined feeling for the relative resemblances and graduated differences that were observed in comparing plants with one another, and this is no less true of the enumeration of natural families attempted by bernard de jussieu in

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1759. to such of these small groups of related forms as had not been already named both linnaeus and jussieu gave names, which they took not from certain marks, but from the name of a genus in each group. but this mode of naming plainly expresses the idea which from that time forward prevailed in systematic botany, that there is a common type lying at the foundation of each natural group, from which all its forms though specifically distinct can be derived, as the forms of a crystal may all be derived from one fundamental form,—an idea which was also expressed by pyrame de candolle in 1819.

but botanists could not rest content with merely naming natural groups; it was necessary to translate the indistinct feeling, which had suggested the groups of linnaeus and bernard de jussieu, into the language of science by assigning clearly recognised marks; and this was from this time forward the task of systematists from antoine laurent de jussieu and de candolle to endlicher and lindley. but it cannot be denied, that later systematists repeatedly committed the fault of splitting up natural groups of affinity by artificial divisions and of bringing together the unlike, as cesalpino and the botanists of the 17th century had done before them, though continued practice was always leading to a more perfect exhibition of natural affinities.

but while natural relationship was thus becoming more and more the guiding idea in the minds of systematists, and the experience of centuries was enforcing the lesson, that predetermined grounds of classification could not do justice to natural affinities, the fact of affinity became itself more unintelligible and mysterious. it seemed impossible to give a clear and precise definition of the conception, the exhibition of which was felt to be the proper object of all efforts to discover the natural system, and which continued to be known by the name of affinity. a sense of this mystery is expressed in the sentence of linnaeus:

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‘it is not the character (the marks used to characterise the genus) which makes the genus, but the genus which makes the character;’ but the very man, who first distinctly recognised this difficulty in the natural system, helped to increase it by his doctrine of the constancy of species. this doctrine appears in linnaeus in an unobtrusive form, rather as resulting from daily experience and liable to be modified by further investigation; but it became with his successors an article of faith, a dogma, which no botanist could even doubt without losing his scientific reputation; and thus during more than a hundred years the belief, that every organic form owes its existence to a separate act of creation and is therefore absolutely distinct from all other forms, subsisted side by side with the fact of experience, that there is an intimate tie of relationship between these forms, which can only be imperfectly indicated by definite marks. every systematist knew that this relationship was something more than mere resemblance perceivable by the senses, while thinking men saw the contradiction between the assumption of an absolute difference of origin in species (for that is what is meant by their constancy) and the fact of their affinity. linnaeus in his later years made some strange attempts to explain away this contradiction; his successors adopted a way of their own; various scholastic notions from the 16th century still survived among the systematists, especially after linnaeus had assumed the lead among them, and it was thought that the dogma of the constancy of species might find especially in plato’s misinterpreted doctrine of ideas a philosophical justification, which was the more acceptable because it harmonised well with the tenets of the church. if, as elias fries said in 1835, there is ‘quoddam supranaturale’ in the natural system, namely the affinity of organisms, so much the better for the system; in the opinion of the same writer each division of the system expresses an idea (‘singula sphaera (sectio) ideam quandam exponit’), and all these ideas might easily be explained in their ideal connection as representing the plan of creation. if observation and theoretical considerations occasionally

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suggested objections to such views, these objections were usually little regarded, and in fact reflections of this kind on the real meaning of the natural system did not often make their appearance; the most intelligent men turned away with an uncomfortable feeling from these doubts and difficulties, and preferred to devote their time and powers to the discovery of affinities in individual forms. at the same time it was well understood that the question was one which lay at the foundation of the science. at a later period the researches of nägeli and others in morphology resulted in discoveries of the greatest importance to systematic botany, and disclosed facts which were necessarily fatal to the hypothesis, that every group in the system represents an idea in the platonic sense; such for instance were the remarkable embryological relations, which hofmeister discovered in 1851, between angiosperms, gymnosperms, vascular cryptogams and muscineae; nor was it easy to reconcile the fact, that the physiologico-biological peculiarities on the one hand and the morphological and systematic characters on the other are commonly quite independent of one another, with the plan of creation as conceived by the systematists. thus an opposition between true scientific research and the theoretical views of the systematists became more and more apparent, and no one who paid attention to both could avoid a painful feeling of uncertainty with respect to this portion of the science. this feeling was due to the dogma of the constancy of species, and to the consequent impossibility of giving a scientific definition of the idea of affinity.

this state of things finally ceased with the appearance of darwin’s first and best book on the origin of species in 1859; from a multitude of facts, some new, but most of them long well-known, he showed that the constancy of species was no longer an open question; that the doctrine was no result of exact observation, but an article of faith opposed to observation. the establishment of this truth was followed almost as a

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matter of course by the true conception of that which had been hitherto figuratively called affinity; the degrees of affinity expressed in the natural system indicated the different degrees of derivation of the varying progeny of common parents; out of affinity taken in a figurative sense arose a real blood-relationship, and the natural system became a table of the pedigree of the vegetable kingdom. here was the solution of the ancient problem.

darwin’s theory has this special interest in the history of the science, that it established clearness in the place of obscurity, a scientific principle in place of a scholastic mode of thought, in the domain of systematic botany and morphology. yet darwin did not effect this change in opposition to the historical development of our science or independently of it; on the contrary his great merit is that he has correctly appreciated the problems long existing in systematic botany and morphology from the point of view of modern research, and has solved them.

that the constancy of species is incompatible with the idea of affinity, that the morphological (genetic) nature of organs does not proceed on parallel lines with their physiological and functional significance, are facts which were known in botany and zoology before the time of darwin; but he was the first to show, that variation and natural selection in the struggle for existence solve these problems, and enable us to conceive of these facts as the necessary effects of known causes; it is at the same time explained, why the natural affinity first recognised by de l’obel and kaspar bauhin cannot be exhibited by the use of predetermined principles of classification, as was attempted by cesalpino.