The examples appended by me to the diagnoses show that with the exception of the sixth, tenth, and fifteenth classes, no one perfectly represents a natural group of the vegetable kingdom. Most of them are a collection of heterogeneous objects, and the distinction of Dicotyledons and Monocotyledons, almost perfectly carried out by de l’Obel and Bauhin, is to a great extent effaced; the ninth class certainly contains only Monocotyledons, but not all of them. This result of great efforts on the part of a mind so well trained as Cesalpino’s is highly unsatisfactory. Not a single new group founded on natural affinities is established, which does not appear already in the herbals of Germany and the Netherlands. It is characteristic of the natural system to reveal itself to a certain extent more readily to instinctive perception than to the critical understanding. We have seen that Cesalpino intended as far as possible to give expression in his system to natural affinities, and the final result was a series of highly unnatural groups, almost every one of which is a collection of the most heterogeneous forms. The cause of this apparently so remarkable fact is this, that he believed that he could establish on predetermined grounds the marks which indicate natural affinities. The uninterrupted labour of nearly 300 years, starting again and again from the same principle or practically under its influence, has given us inductive proof that the path taken by Cesalpino is the wrong one. And if, while this path was pursued even into the middle of the 18th century, we see natural groups emerge with increasing distinctness, it is because the botanist, though on the wrong track, was still continually gaining better acquaintance with the ground over which he was wandering, and attained at length to an anticipation of the truer way.
Joachim Jung[20] was born in Lübeck in the year 1587, and died after an eventful life in 1657. He was a contemporary of Kepler, Galileo, Vesal, Bacon, Gassendi, and Descartes. After having been already a professor in Giessen, he applied himself to the study of medicine in Rostock, was in Padua in 1618 and 1619, and there, as we may confidently believe, became acquainted with the botanical doctrines of Cesalpino, who had died fifteen years before. Returning to Germany, he held various professorships during the succeeding ten years in Lübeck and Helmstädt, and became Rector of the Johanneum in Hamburg in 1629. He occupied himself with the philosophy of the day, in which he appeared as an opponent of scholasticism and of Aristotle, and also with various branches of science, mathematics, physics, mineralogy, zoology, and botany. In all these subjects he displayed high powers as a student and a teacher, and especially as a critical observer; in botany at least he was a successful investigator. He was the first in Germany, as Cesalpino had been in Italy, who combined a philosophically educated intellect with exact observation of plants.
His pupils were at first the only persons who profited by his botanical studies, for with his many occupations and a perpetual desire to make his investigations more and more complete he himself published nothing. In 1662 his pupil Martin Fogel printed the ‘Doxoscopiae Physicae Minores,’ a work of enormous compass left in manuscript at the master’s death, and another pupil, Johann Vagetius, the ‘Isagoge Phytoscopica,’ in 1678. Ray however tells us that a copy of notes on botanical subjects had already reached England in 1660. The ‘Doxoscopiae’ contains a great number of detached remarks on single plants and on their distinguishing marks, and propositions concerning the methods and principles of botanical research,—all in the form of aphorisms which he had from time to time committed to paper. The number and contents of these aphorisms show the earnest attention which he bestowed on the determination of species; he is displeased that so many botanists devote more time and labour to the discovery of new plants, than to referring them carefully and logically to their true genera by means of their specific differences. He was the first who objected to the traditional division of plants into trees and herbs, as not founded on their true nature. But how firmly this old dogma was established is well shown by the fact, that Ray at the end of the century still retained this division, though he founded his botanical theories on the ‘Isagoge’ of Jung. Jung was in advance of Cesalpino and his own contemporaries in repeatedly expressing his doubt of the existence of spontaneous generation.
The ‘Isagoge Phytoscopica,’ a system of theoretical botany, very concisely written and in the form of propositions arranged in strict logical sequence, was a more important work and had more lasting effects upon the history of botany. We must look more closely into the contents of this volume, because it contains the foundation of the terminology of the parts of plants subsequently established by Linnaeus. Since the matter of the ‘Isagoge’ is produced in Ray’s ‘Historia Plantarum’ in italics, with special mention of the source from which it is derived, it cannot be doubted that Linnaeus had made acquaintance with the teaching of Jung as a young man, in any case before 1738. It is as important as a matter of history to know that Linnaeus’ terminology is founded on Jung, as it is to learn that his most general philosophical propositions on botanical subjects are to be traced to Cesalpino. It will moreover be fully shown in the account of the doctrine of sexuality that his knowledge of that subject was derived from Rudolf Jacob Camerarius.
The first chapter of the ‘Isagoge’ discusses the distinction between plants and animals. A plant is, according to Jung, a living but not a sentient body; or it is a body attached to a fixed spot or a fixed substratum, from which it can obtain immediate nourishment, grow and propagate itself. A plant feeds when it transforms the nourishment which it takes up into the substance of its parts, in order to replace what has been dissipated by its natural heat and interior fire. A plant grows when it adds more substance than has been dissipated, and thus becomes larger and forms new parts. The growth of plants is distinguished from that of animals by the circumstance that their parts are not all growing at the same time, for leaves and shoots cease to grow as soon as they arrive at maturity; but then new leaves, shoots, and flowers are produced. A plant is said to propagate itself when it produces another specifically like itself; this is the idea in its broader acceptation. We see that here, as in Cesalpino, the idea of the species is connected with that of propagation. The second chapter, headed ‘Plantae Partitio,’ treats of the most important morphological relations in the external differentiation of plants; here Jung adheres essentially to Cesalpino’s view, that the whole body in all plants, except the lowest forms, is composed of two chief parts, the root as the organ which takes up the food, and the stem above the ground which bears the fructification. Jung, too, draws attention to the meeting-point of the two parts, Cesalpino’s ‘cor,’ but under the name of ‘fundus plantae.’
The upper part, or a portion of the plant, is either a stem, a leaf, a flower, a fruit, or a structure of secondary importance, such as hairs and thorns. His definition of the stalk and the leaf is noteworthy; the stalk, he says, is that upper part which stretches upwards in such a manner, that a back and front, a right and left side, are not distinguished in it. A leaf is that which is extended from its point of origin in height, or in length and breadth, in such a manner, that the bounding surfaces of the third dimension are different from one another, and therefore the outer and inner surfaces of the leaf are differently organised. The inner side of the leaf, which is also called the upper, is that which looks towards the stem, and is therefore concave or less convex than the other side. One conclusion he draws, which is a striking one for that time, that the compound leaf is taken for a branch by inexperienced or negligent observers, but that it may easily be determined by having an inner and an outer surface, like the simple leaf, and by falling off as a whole in autumn. He calls a plant ‘difformiter foliata,’ whose lower leaves are strikingly different from the upper, an idea which Goethe, in the fragment in Guhrauer, seems to have altogether misunderstood.
In connection with these general definitions, the different forms of the stem and of the ramification, and the varieties of leaves are pointed out and supplied with distinctive names, which are for the most part still in use. The fourth chapter treats of the division of the stem into internodes; if the stem or branch, says Jung, is regarded as a prismatic body, the articulations, that is, the spots where a branch or a leaf-stalk arises, are to be conceived of as cross-sections parallel to the base of the prism. These spots when they are protuberant are called knees or nodes, and that which lies between such spots is an internode.
It is not possible to quote all the many excellent details which follow these definitions; but some notice must be taken of Jung’s theory of the flower, which he gives at some length from the 13th to the 27th chapters. It suffers, as in Cesalpino, from his entire ignorance of the difference of sexes in plants, which is sufficient to render any satisfactory definition of the idea of a flower impossible. Like Cesalpino too he distinguishes the pistil from the flower, instead of making it a part of the flower. He regards the flower as a more delicate part of the plant, distinguished by colour or form, or by both, and connected with the young pistil. Like all botanists up to the end of the 18th century, he follows Cesalpino in including under the term fruit both the dry indehiscent fruits which were supposed to be naked seeds, and any seed-vessel. He differs from him in calling the stamens ‘stamina,’ and the style ‘stilus,’ but like Cesalpino he uses the word ‘folium’ for the corolla. He calls a flower perfect only when it has all these three parts. He afterwards describes the relations of form and number in the parts of the flower, and among other things he enunciates the first correct view of the nature of the capitulum in the Compositae, which Cesalpino quite misunderstood; and he examined inflorescences and superior and inferior flowers, which Cesalpino had already distinguished, with more care than they had previously received. In his theory of the seed he follows Cesalpino, and adds nothing to him.
There is nothing which more essentially distinguishes the theoretical botany of Jung, and marks the advance which he made upon Cesalpino’s views, than the way in which he discusses morphology in as entire independence as was possible of all physiological questions, and therefore abstains from teleological explanations. His eye is fixed on relations of form only, while his mode of treating them is essentially comparative, and embraces the whole of the vegetable kingdom that was known to him. Jung certainly learnt much from Cesalpino; but in rejecting at least the grosser aberrations of the Aristotelian philosophy and of scholasticism, he freed himself from the prepossessions of his master, and succeeded in arriving at more correct conceptions of the morphology of plants. That his mathematical gifts assisted him in this respect is easy to be gathered from his definitions as given above, which bring into relief the symmetry apparent in the forms of stems and leaves. No more profound or apt definitions were supplied till Schleiden and Nägeli introduced the history of development into the study of morphology.
While Cesalpino, Kaspar Bauhin, and Jung stand as solitary forms each in his own generation, the last thirty years of the 17th century are marked by the stirring activity of a number of contemporary botanists. While during this period physics were making rapid advances in the hands of Newton, philosophy in those of Locke and Leibnitz, and the anatomy and physiology of plants by the labours of Malpighi and Grew, systematic botany was also being developed, though by no means to the same extent or with equally profound results, by Morison, Ray, Bachmann (Rivinus), and Tournefort. The works of these men and of their less gifted adherents, following rapidly upon or partly synchronous with each other, led to an exchange of opinions and sometimes to polemical discussion, such as had not before arisen on botanical subjects; this abundance of literature, with the increased animation of its style, excited a more permanent interest, which spread beyond the narrow circle of the professional adepts. The systematists above-named endeavoured to perfect the morphology and the terminology of the parts of plants, and they found ready to their hands in the works of their predecessors a considerable store of observations and ideas, upon which they set themselves to work. A very great number of descriptions of individual plants had been accumulated since the time of Fuchs and Bock, and the fact of natural affinity had been recognised in the ‘Pinax’ of Kaspar Bauhin as the foundation of a natural system; Cesalpino had pointed to the organs of fructification as the most important for such a system, and Jung had supplied the first steps to a comparative morphology in place of a mere explanation of names. The botanists of the last thirty years of the 17th century could not fail to perceive that the series of affinities as arranged by de l’Obel and Bauhin could not be defined by predetermined marks in the way pursued by Cesalpino, nor fashioned in this way into a well-articulated system. Nevertheless they held fast in principle to Cesalpino’s mode of proceeding, though they endeavoured to amend it by obtaining their grounds of division, not as he had done, chiefly from the organisation of the seed and fruit, but from other parts of the flower; variations in the corolla, the calyx, and the general habit were employed to found systems, which were intended to exhibit natural affinities. And while the true means were thus missed, the end itself was not clearly and decidedly adhered to; a system was desired for the purpose of facilitating the acquisition of a knowledge of the greatest possible number of individual forms; the weight of the burden caused by the foolish demand that every botanist should know all described plants, was continually increasing, and naturally led to seeking some alleviation in systematic arrangement. Excessive devotion to the describing of plants stood in the way of such a profound study of the principles of systematic botany as might have led to enduring results, and even destroyed the very capacity for those difficult intellectual operations, which were absolutely necessary to build up a truly natural system on scientific foundations; the wood could not be seen for the trees. Above all the morphology founded by Jung, though acknowledged and employed, was not sufficiently developed by the labours of others to form the foundation of the system in its grander features,—a reproach which must be made against the systematists of the succeeding hundred years with few exceptions. How could the botanists of the 17th century succeed in acquiring a true conception of the larger groups indicated by natural affinity, when they still held to the old division into trees and herbs, which Jung had already set aside and which is opposed to all consistent morphology, and when they paid so little attention to the structure of the seed and the fruit, that they commonly treated dry indehiscent fruits as naked seeds, and were guilty of other and similar mistakes? But if nothing new and good in principle found its way into systematic botany, much service was rendered to it in matters of detail. The working out of various systems helped to show what marks are not admissible in fixing the limits of the natural groups; the contradiction between the method and aim of the systematists became in this empirical way continually more apparent, till at length Linnaeus was able to recognise it distinctly; and this was beyond doubt a great gain.