4. Species has miscuit casus, unde totidem quot passim occurrunt varietates.

Hugo Mohl was right in rejecting Heufler’s assumption that a view resembling the modern theory of descent was contained in these paragraphs. It must be plain to any one who knows the ideas of Aristotle, Theophrastus, and Cesalpino, within the sphere of which Linnaeus is here moving, what he understands by his ‘vegetabile medullare’ and ‘corticale’; that he does not for a moment mean a plant of simplest organisation, but that both expressions indicate only the original elements of vegetation which the Creator, according to Linnaeus, united to one another at the first. He assumed that plants of the highest and of the lowest grades of organisation were originally created at the same time and alongside of one another; no new class-plants were afterwards created, but from the mingling together of the existing ones by the act of the Creator generically distinct forms were produced, and the natural mingling of these gave birth to species, while varieties were mere chance deviations from species. But it is to be noticed that in these minglings or hybridisations the woody substance of the one form which supplies the pollen is united with the pith-substance of the other form, whose pistil is thus fertilised; and so in these supposed crossings it is always the two original elements of the plant, the medullary and the cortical, which are mingled together.

No further proof is wanting that this theory of Linnaeus is no precursor of our theory of descent, but is most distinctly opposed to it; it is utterly and entirely the fruit of scholasticism, while the essential feature in Darwin’s theory of descent is that scholasticism finds no place in it.

[CHAPTER III.]
Development of the Natural System under the Influence of the Dogma of the Constancy of Species.
1759-1850.

From the year 1750 Linnaeus’ terminology of the organs of plants and his binary method of naming species came into general use; the opposition which his doctrines had till then encountered by degrees died away, and if all that he taught was not universally accepted, his treatment of the art of describing plants soon became the common property of all botanists.

But in course of time two very different tendencies were developed; most of the German, English, and Swedish botanists adhered strictly to Linnaeus’ dictum, that the merit of a botanist was to be judged by the number of species with which he was acquainted; they accepted Linnaeus’ sexual system as one that completed the science in every respect; they thought that botany had reached its culminating point in Linnaeus, and that any improvement or addition could only be made in details, by continuing to smooth over some unevennesses in the system, to collect new species and describe them. The inevitable result was that botany ceased to be a science; even the describing of plants which Linnaeus had raised to an art became once more loose and negligent in the hands of such successors; in place of the morphological examination of the parts of plants there was an endless accumulating of technical terms devoid of depth of scientific meaning, till at length a text-book of botany came to look more like a Latin dictionary than a scientific treatise. In proof of this we may appeal to Bernhardi’s ‘Handbuch der Botanik,’ published at Erfurt in 1804, and Bernhardi was one of the best representatives of German botany of the time. How botany, especially in Germany, gradually degenerated under the influence of Linnaeus’ authority into an easy-going insipid dilettantism may very well be seen from the botanical periodical, entitled ‘Flora,’ the first volumes of which cover the greater part of the first fifty years of the 19th century; it is scarcely conceivable how men of some cultivation could occupy themselves with such worthless matter. It would be quite lost labour to give any detailed account of this kind of scientific life, if it can be so called, this dull occupation of plant-collectors, who called themselves systematists, in entire contravention of the meaning of the word. It is true indeed that these adherents of Linnaeus did some service to botany by searching the floras of Europe and of other quarters of the globe, but they left it to others to turn to scientific account the material which they collected.

But before this evil had spread very widely, a new direction to the study of systematic botany and morphology was given in France, where the sexual system had never met with great acceptance. Bernard de Jussieu and his nephew, Antoine Laurent de Jussieu, taking up Linnaeus’ profounder and properly scientific efforts, made the working out of the natural system, in Linnaeus’ own opinion the highest aim of botany, the task of their lives. Here more was needed than a perpetual repetition of descriptions of single plants after a fixed pattern; more exact inquiries into the organisation of plants, and especially of the parts of the fructification, must supply the foundation of larger natural groups. It was a question therefore of new inductive investigation, of real physical science, of penetrating into the secrets of organic form, whereas the botanists who confined themselves to Linnaeus’ art of description made no new discoveries respecting the nature of plants. And if these men held to the dictum just quoted from Linnaeus, and therefore regarded themselves as his genuine disciples, the founders of the natural system had as good a right to the title, not because they followed his nomenclature and method of diagnosis, but because they strove after exactly that object which he had placed first in the science, the construction of the natural system; they were really the men whom he had meant when he spoke of ‘methodici’ and ‘systematici.’ The German, English, and Swedish collectors of plants adhered to the less profound, every-day, practical precepts of their master; the founders of the natural system followed the deeper traces of his knowledge. This direction proved to be the only one endowed with living power, the true possessor of the future.

The efforts of Jussieu, Joseph Gärtner, De Candolle, Robert Brown, and their successors up to Endlicher and Lindley, are not marked only by the fact that they did truly seek to exhibit the gradations of natural affinities by means of the natural system; equally characteristic of these men is their firm belief in the dogma of the constancy of species as defined by Linnaeus. Here at once was a hindrance to their efforts; the idea of natural relationship, on which the natural system exclusively rests, necessarily remained a mystery to all who believed in the constancy of species; no scientific meaning could be connected with this mysterious conception; and yet the farther the inquiry into affinities proceeded, the more clearly were all the relations brought out, which connect together species, genera, and families. Pyrame de Candolle developed with great clearness a long series of such affinities as revealed to us by comparative morphology, but how were these to be understood, so long as the dogma of the constancy of species severed every real objective connection between two related organisms? Little indeed could be made of these acknowledged affinities; still, in order to be able to speak of them and describe them, recourse was had to indefinite expressions, to which arbitrary and figurative meanings could 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 dari in vegetabilibus negat generatio continuata, propagatio, observationes quotidianae, cotyledones.’

In spite of all this one important advance was made by the successors of Jussieu; the larger groups of genera, the families, were defined with the certainty and precision, with which Linnaeus had fixed the boundaries of species and genera, and were supplied with characteristic marks. They succeeded also in clearly distinguishing various still larger groups founded on natural affinity, such as the Monocotyledons and Dicotyledons; the distinction between Cryptogams and Phanerogams was by degrees better appreciated, though this point could not be finally settled, so long as it was attempted to reduce the Cryptogams entirely to the scheme of the Phanerogams. The chief hindrance however to the advance of systematic botany, at least at the beginning of this period, lay in the defective morphology enshrined in Linnaeus’ terminology and in his doctrine of metamorphosis. A great improvement certainly was effected in the early part of the 19th century by De Candolle’s doctrine of the symmetry of plants,—a doctrine which has been much undervalued, and that merely on account of its name; it is really a comparative morphology, and the first serious attempt of the kind since the time of Jung that has produced any great results; a series of the most important morphological truths, with which every botanist is now conversant, were taught for the first time in De Candolle’s doctrine of symmetry in 1813. But one thing was wanting not only in Jussieu and De Candolle, but in all the systematists of this period, with the single exception of Robert Brown, and this was the history of development. The history of the morphology and systematic botany of this period shows indeed, that the comparison of mature forms leads to the recognition of many and highly important morphological facts; but as long as matured organisms only are compared, the morphological consideration of them is always disturbed by the circumstance that the organs to be compared are already adapted to definite physiological functions, and thus their true morphological character is often entirely obscured; on the other hand, the younger the organs are, the less is this difficulty experienced, and this is the real reason why the history of development is of so great service to morphology. It was then one of the characteristic features of the period we are describing, that its morphology was formed upon the study of matured forms; the history of development, or at all events of very early stages of development, could not be turned to account till after 1840, for skill in the use of the microscope, here indispensable, was not sufficiently advanced before that time to make it possible to follow the growth of organs from their first beginnings.