History of botany (1530–1860)/Book 1/Chapter 4

by Julius von Sachs

CHAPTER IV.

Morphology Under the Influence Of the Doctrine Of Metamorphosis and Of the Spiral Theory.

1790–1850.

The efforts of Jussieu, De Candolle, and Robert Brown were directed to the discovery of the relationship between different species of plants by comparing them together; the doctrine of metamorphosis founded by Goethe set itself from the first to bring to light the hidden relationship between the different organs of one and the same plant. As De Candolle's doctrine of symmetry derived the different species of plants from an ideal plan of symmetry or type, so the doctrine of metamorphosis assumed an ideal fundamental organ, from which the different leaf-forms in a plant could be derived. The stem came into consideration only as carrying the leaves, the root was almost entirely disregarded. As the resemblance of nearly allied species of plants suggests itself naturally and unsought to the mind of the unbiassed observer, so also does the connection between different organs of a leafy nature in one and the same plant. Cesalpino called the corolla simply a 'folium' (leaf); he and Malpighi regarded the cotyledons also as leaves; Jung called attention to the variety of the leaf-forms, which are found in many plants at different heights on the same stem; Caspar Friedrich Wolff, the first who bestowed systematic consideration on the subject, declared in 1766, that he saw nothing ultimately in the plant but leaves and stem, including the root in the stem^[1].

Long before Goethe's time speculation had busied itself with attempts to explain these observations; we saw how Cesalpino and Linnaeus, starting from the old view that the pith is the seat of the soul in plants, regarded the seeds as metamorphosed pith, the floral envelopes with the stamens and the true leaves as metamorphosed layers of the rind and wood of the stem. The word metamorphosis from their point of view had a very plain meaning; it was really the cylindrical pith whose upper end changed into seeds, it was the actual substance of the cortex which produced both the ordinary leaves and the parts of the flower. Wolff on the other hand from a point of view of his own gave an apparently intelligible physical explanation of the proposition, that all appendages of the stem are leaves, but the explanation had the fault of not being true; he attributed the metamorphosis of leaves to altered nourishment, the flowers especially to his 'vegetatio languescens.'

Goethe's conception of the matter was from the first much less clear, and chiefly because he was never able to bring the abnormal into its true connection with the normal or ascending metamorphosis. In the first sentence of his 'Doctrine of metamorphosis' (1790) he says, 'that it is open to observation that certain exterior parts of plants sometimes change and pass into the form of adjacent parts, either wholly or in a greater or less degree.' In the cases of which Goethe is here thinking a distinct meaning can be affixed to the word metamorphosis; if, for example, the seeds of a plant with normal flowers produce a plant which has petals in place of stamens, or in which the ovaries are resolved into green expanded leaves, it is actually the case that a plant of a known form has given rise to another plant of a different form, in other words, a change or metamorphosis has really taken place. But we cannot reason in this way in the case of that which Goethe calls normal or ascending metamorphosis. When in a given species, which has remained constant with all its marks for countless generations, the cotyledons, the leaves, the bracts, and the parts of the flower are called leaves, this must be merely the result of abstraction, which has led to the generalising of the idea of a leaf; if we make abstraction of the physiological characters of the carpels, stamens, floral envelopes, and cotyledons, and regard only the way in which they originate on the stem, we are justified in including them in one general idea with ordinary leaves, and to this idea we quite arbitrarily give the name leaf. But this does not justify us in speaking of a change of these organs, so long as we consider the whole plant in question as a hereditary and constant form. For the plant therefore taken as constant the idea of metamorphosis has only a figurative meaning; the abstraction performed by the mind is transferred to the object itself, if we ascribe to it a metamorphosis which has really taken place only in our conception. The case would be different, if here as well as in the abnormal instances above-mentioned we could assume that the stamens and other organs of the plants lying before us were ordinary leaves in their progenitors. So long as this assumption of an actual change is not even hypothetically made, the expression change or metamorphosis is purely figurative, the metamorphosis is a mere 'idea.' This distinction Goethe has not made; he did not clearly see that his normal ascending metamorphosis can only have the meaning of a scientific fact, if a real change is assumed to take place in the course of propagation in this case, as in that of abnormal metamorphosis or misformation. A comparison of his various expressions shows that he took the word metamorphosis sometimes in its literal, sometimes in its ideal and figurative sense; for instance, he says expressly, 'We may say that a stamen is a folded petal, just as we may say that a petal is a stamen in a state of expansion.' This sentence shows that Goethe did not regard a particular leaf-form as first in time, and that others proceeded from it by change; he uses the word metamorphosis in a purely ideal sense. At other times his remarks may be interpreted as though he really considered the normal ascending metamorphosis to be a real change in the organs, arising from a transmutation of the species. With this confusion of notion and thing, idea and reality, subjective conception and objective existence, Goethe took up exactly the position of the so-called nature-philosophy.

Goethe's doctrine could only make its way to logical consistency and clearness of thought by deciding for the one or the other way; he must either assume that the different leaf-forms, which were regarded as alike only in the idea, were really produced by change of a previous form,—a conception that at once presupposes a change of species in time; or he must entirely adopt the position of the idealistic philosophy, in which idea and reality coincide. In this case the assumption of a change in time was not necessary; the metamorphosis remained an ideal one, a mere mode of view; the word leaf then signifies only an ideal fundamental form from which the different forms of leaves actually observed may be derived, as De Candolle's constant species from an ideal type.

If now we read Goethe's further remarks on the doctrine of metamorphosis attentively^[2], we perceive that he really arrived at neither of these conclusions, but perpetually vacillated between the two; a number of his sayings might be collected, which might be taken for precursors of a theory of descent, as they have been taken by some modern writers; but it is quite as easy to make a selection which would carry us back to the position of the ideal philosophy and the constancy of species. In the later years of his life the idea of a physical metamorphosis accomplished in time, and involving a change of species, does appear more distinctly in Goethe's writings. This explains the lively, nay passionate, interest which he took in the dispute between Cuvier and Geoffrey de St. Hilaire in 1830^[3] We gather from it that Goethe, in spite of all his wanderings in the mists of the nature-philosophy of the time, felt a growing need for some clearer insight into the nature of metamorphosis, both in plants and animals, without ever being able to make his way into the clear light.

But these better motions remained without importance for the history of botany; the adherents of his doctrine of metamorphosis all apprehended it in the sense of the nature-philosophy, and Goethe himself did not remonstrate against the frightful way in which it was distorted by them. Its further development therefore was in accordance with the principles of that philosophy, which was accustomed to apply the results of purely idealistic views in an uncritical way to imperfectly observed facts. Above all the difficulty remained unsolved, how the dogma of the constancy of species was to be brought into logical connection with the idea of the metamorphosis of organs. The supranatural, which Elias Fries found in the natural system, subsisted still in the doctrine of metamorphosis in comparing the organs of a plant.

Still more obscure and entirely the product of the nature-philosophy is Goethe's view of the spiral tendency in vegetation. At p. 194 of his essay entitled 'Spiraltendenz der Vegetation' (1831) he says: 'Having fully grasped the idea of metamorphosis we next turn our attention to the vertical tendency, in order to gain a nearer acquaintance with the development of the plant. This tendency must be looked upon as an immaterial staff, which supports the existence . . . . This principle of life (!) manifests itself in the longitudinal fibres which we use as flexible threads for many purposes; it is this which forms the wood in trees, which keeps annual and biennial plants erect, and even produces the extension from node to node in climbing and creeping plants. Next we have to observe the spiral direction which winds round the other.' This spiral direction which passes at once with Goethe into a 'spiral tendency,' is seen in various phenomena of vegetation, as in spiral vessels, in twining stems, and sometimes in the position of leaves. The closing remarks of this short essay, in which he explains the vertical tendency as the male, the spiral as the female principle in the plant, show how far Goethe lost himself in the profundities of the nature-philosophy. Thus he introduced his readers into the deepest depths of mysticism.

It would be as useless as it would be wearisome to follow out in detail to its extremest point of absurdity the progressive transformation which the doctrine of metamorphosis underwent in the hands of the botanists of the nature-philosophy school, and to see how its catchwords, polarity, contraction and expansion, the stem-like and the fistular, anaphytosis and life-nodes, and others, were compounded with the results of the most every-day observation into meaningless conglomerates; rough obscure impressions of the sense, as well as incidental fancies, were regarded as ideas and principles. A full account of these inconceivable aberrations is to be found in Wigand's 'Geschichte und Kritik der Metamorphose.' Our own countrymen certainly, Voigt, Kieser, Nees von Esenbeck, C. H. Schulz, and Ernst Meyer (the historian of botany) bear off the palm of absurdity, but there were others also, among them the Swedish botanist Agardh, and many Frenchmen, Turpin, for instance, and Du Petit-Thouars^[4], who were not altogether free from this weakness. Even the best German botanists of the time, such as Ludolph Treviranus, Link, G. W. Bischoff, and others, managed to escape the influence of this philosophy of nature, only where they confined themselves to the most barren empiricism. Strange phenomenon! that as soon as gifted and understanding men began to talk of the metamorphosis of plants, they fell into senseless phrase-mongering; Ernst Meyer, for instance, was it is true no great botanist, but he shows in his 'Geschichte der Botanik' that he possessed a clever and cultivated intellect. The painful impression, which the treatment of the doctrine of metamorphosis by these writers makes upon us, is due partly to the fact that the deeper meaning of the idealistic philosophy never attained to logical expression in their hands, and still more to their indulgence in an unmeaning play of phrases, combining the highest abstractions with the most negligent and rudest empiricism, and sometimes with utterly incorrect observations. Oken can claim the merit of more correct observation and greater philosophical consistency, and if we reject his views, yet his mode of presenting them has at least the pleasing appearance of more consequential reasoning. We perceive for the first time the full greatness of the debt which modern botany owes to men like Pyrame de Candolle, Robert Brown, von Mohl, Schleiden, Nägeli, and Unger, the latter of whom only slowly worked his way out of the trammels of the nature-philosophy, when we compare the literature of the doctrine of metamorphosis before the year 1840 with the present condition of our science, for which they paved the way.

In spite of the real and apparent differences between Goethe's doctrine of metamorphosis and De Candolle's doctrine of a plan of symmetry, these writers agreed in this, that they set out alike from the doctrine of the constancy of species, and led up equally to the result, that alongside of manifold physiological differences in the organs of plants certain points of formal agreement can be discovered, which are expressed chiefly in the order of their succession and in their relative positions. In this distinction lay the good kernel of the doctrine of metamorphosis in Goethe, and Wolff, and even in Linnaeus and Cesalpino: it was only necessary to set this free from the dross with which the nature-philosophy had surrounded it, and to make the relations of position in organs the subject of earnest investigation, in order to secure important results in this branch of morphology. The first step in this direction was taken by Carl Friedrich Schimper, who was followed by Alexander Braun; both adopted the main idea of the doctrine of metamorphosis in the form in which it can be reconciled with the doctrine of constancy, that is, in a purely idealistic sense. Both liberated themselves from the gross errors of the nature-philosophers, and thus gave a more logical expression to the purely idealistic morphological consideration of form in plants.

Karl Friedrich Schimper^[5] founded before the year 1830 the theory of the arrangement of leaves which is named after him, and which he expounded to the naturalists assembled at Stuttgart in 1834 as a complete and perfected system. Alexander Braun, in a review of Schimper's exposition in 'Flora' of 1835, gave a clear and simple account of the theory, having already himself published an excellent and comprehensive treatise on the same subject. The doctrine of phyllotaxis appeared in these publications with a formal completeness which could not fail to attract the attention of the botanical world and indeed of a larger audience; and justly so, for, as unfortunately so very seldom happens in botanical subjects, a scientific idea was in this case not merely incidentally suggested, but was worked out in all its consequences as a complete structure, and this structure gained in external splendour from the circumstance that its propositions, dealing with geometrical constructions, could be expressed in numbers and formulae, a thing hitherto unknown in botanical science.

That the leaves are arranged on the stems that produce them according to fixed geometrical rules had been noticed by Cesalpino and by Bonnet in the middle of the eighteenth century; but nothing more resulted than weak attempts at mere description of different cases. Schimper's theory is marked by that which is at once its greatest merit and its fundamental error, the referring of all relations of position to a single principle. This principle lies in the idea that growth in a stem has an upward direction in a spiral line, and that the formation of leaves is a local exaggeration of this spiral growth. The direction of the spiral line may change in the same species, or in the same axis, and may even change from leaf to leaf. The important variations in the arrangement of leaves are not shown in their longitudinal distances, but in the measure of their lateral deviations on the stem. The characteristic point in this theory is the mode of considering these lateral deviations or divergences of the leaves as they follow one another on an axis, the referring them to a more general law of position. Means were at the same time skilfully supplied for discovering the true conditions of arrangement, the genetic spiral, in cases where the genetic succession of the leaves, and consequently their divergence, could not be immediately recognised. After innumerable observations, it appeared that there is a wonderful variety in the disposition of leaves, but that at the same time a comparatively small number of these variations commonly occur, and that these ordinary divergences, ¹⁄₂, ²⁄₃, ³⁄₈, ⁸⁄₁₃, ¹³⁄₂₁, etc. have this remarkable relation to one another, that both the numerator and denominator of each successive fraction are obtained by adding together the numerators and denominators of the two preceding fractions, or the individual fractions named are the successive convergents of a continuous fraction:—

${\frac {1}{1+{\frac {1}{1+{\frac {1}{1\dots }}}}}}$

By change of single cyphers in this, the simplest of all continuous fractions, the expressions were also obtained for all measures of position that deviate from the usual main series. The common occurrence of so-called leaf-whorls seemed at once to be opposed to the principle of special growth and to the doctrine of position founded upon it, especially in the cases in which it was supposed that all the leaves of a whorl arise simultaneously. But the founders of the doctrine, relying on their geometrical constructions, declared that every theory is incorrect, which sets out from the whorl as a simultaneous formation. But the way in which the different leaf-whorls of a stem are arranged among themselves, and are connected with continuous spiral positions, required new geometrical constructions; it was necessary to assume a supplementary relation (prosenthesis), which the measure of the phyllotaxis adopts in the transition from the last leaf of one cycle to the first of the next. Artificial as this construction appears, it has the advantage of saving the spiral principle, and the prosenthetic relation itself admits of being again expressed in highly simple fractions,—a great advantage for the formal consideration of the relative positions of the parts of the flower, and their relation to the preceding positions of the leaves. The great skill shown by the founders of the doctrine in the morphological consideration of the whole plant-form appears equally in the establishment of the rules, according to which the relations of position of the leaves of a side-shoot connect with those of the mother-axis, and which made it possible to represent the nature of inflorescences especially with extreme clearness by means of geometrical figures. An expressive and elegant terminology not only made the whole theory attractive, but fitted it in a high degree to supply a suitable, plain, and precise phraseology for describing the most varied forms of plants. That the theory possesses such advantages as these may be gathered from the fact, that since 1835 the morphological examination and comparison not only of flowers and inflorescences, but also of vegetative shoots and their ramification, has reached great formal completeness. A thorough acquaintance with the principle of this doctrine has made it possible to explain to reader or hearer the most intricate forms of plants so clearly, that they may be said to reveal the law of their formation themselves, and to grow before the eye of the observer, while at the same time the most recondite relations of the organs of the same or of different plants were brought out distinctly and in elegant phraseology. When this mode of description was combined with De Candolle's views on abortion, degeneration, and adherence, and at the same time took into consideration the chief physiological forms of leaf-structures, according as these were developed as scales, foliage-leaves, bracts, floral envelopes, staminal and carpellary leaves, it was possible to give such an artistic account of every form of plant, as made it visible to sense in its entirety, and at the same time brought out the morphological law of its construction. Whoever reads the writings of Alexander Braun and Wydler, and especially of Thilo Irmisch (after 1873), who knew how to combine his descriptions in a variety of ways with remarks on the biological relations of plants, cannot fail to admire the extraordinary skill displayed by these men in describing plants. Compared with the dry diagnoses of the systematists, their descriptions attain to the dignity of an art, and present the commonest forms to the reader in a new and attractive light. But the theory had a further advantage; it seemed not only to present the form of the plant in its matured state, but to treat it genetically; and in fact it did possess an element of historical development, inasmuch as it made the genetic succession of the leaves and of their axillary shoots, which is at the same time the succession from the base to the summit, the foundation of all consideration of the plant-form. But it is also true that in this lay one of the weak sides of the theory; as long as it was a question only of continuous spirals, the succession of matured leaves does also represent the succession of their formation in time; but this was not actually proved in the case of leaf-whorls, and here, to save the theory, genetic relations had to be pre-supposed for which no further proof was forthcoming, while fresh researches have repeatedly shown that a strict application of Schimper's theory is found frequently to contradict the facts of development as directly observed^[6]. Moreover, regard was had only to those measurements of divergence on the continuous genetic spiral which were taken on the matured stem, while there was always the possibility that the divergences might have been different at the first, and been afterwards modified, as Nägeli subsequently suggested^[7]. And again, the theory had a dangerous adversary to encounter in the frequent occurrence of leaves that are strictly alternate or crossed in pairs, and to conceive of this as a spiral arrangement must at once appear to be an arbitrary proceeding both from the mathematical point of view and from that of historical development; the assumption of a return of the genetic spiral from leaf to leaf, as for instance in the Grasses, like the prosenthesis in the change of divergence, afforded, it is true, a construction which was geometrically correct, but which could hardly be made to agree with the history of development and the mechanical forces concerned. Again, it was a great and essential defect in the theory, that in assuming the spiral arrangement it entirely neglected the relations of symmetry of the plant-form, which are in many cases clearly expressed, and their connection with the outer world, on which Hugo von Mohl had already published some excellent remarks in 1836,—a defect, which unhappily is not yet sufficiently appreciated. A due consideration of these objections, and of the cases in which the history of development is opposed to the constructions of the theory, must have led to the conviction that the idea of a spiral tendency in the growth of plants is at least not borne out in all cases, and more profound reflexion would show, that a scientific principle, really explaining the phenomena, is no more to be found in the assumption of such a general tendency, than in a like assumption with regard to the heavenly bodies, that they have a tendency to elliptic movement because they commonly move in ellipses. Hence Hofmeister, the latest investigator of the doctrine of phyllotaxis on the basis of the history of development, comes to the conclusion that the notion of a screw-shaped or spiral course of evolution of lateral members of plants is not merely an unsuitable hypothesis, but an error. Its unreserved abandonment is, he considers, the first condition for attaining an insight into the proximate causes of the varieties of relative position in the vegetable kingdom. But this judgment, correct as it is, was pronounced thirty years after the appearance of Schimper's theory; history, which speaks from another point of view, and not only enquires into the correctness of a theory but has to appraise its historical importance, speaks in a less unfavourable manner. The chief point here is not whether the theory was right, but how far it contributed to the advance of the science. It was distinctly fruitful in results, for it brought the important question of the relative positions of organs for the first time into the front rank in the study of morphology; we may even say that a large part of the results of the study of the history of development were first brought into the true light by the consistent application of the theory, or in the effort to disprove it. With all its fundamental errors, Schimper's theory remains one of the most interesting phenomena in the history of morphology, because it was carried out with thorough logical consistency. We should as little wish to omit it from our literature, as modern astronomy would wish to see the old theory of epicycles disappear from its history. Both theories served to connect together the facts that were known in their time.

The fundamental error of the theory lies much deeper than appears at first sight. Here too we have the idealistic conception of nature, which refuses to know anything of the causal nexus, because it takes organic forms for the ever-recurring copies of eternal ideas, and in accordance with this platonic sphere of thought confounds the abstractions of the mind with the objective existence of things. This confusion shows itself in Schimper's doctrine, inasmuch as he takes the geometrical constructions, which he transfers to his plants and which, though they may be highly suitable from his point of view, are nevertheless purely arbitrary, for actual characters of the plants themselves, in other words, takes the subjective connection of the leaves by a spiral line for a tendency inherent in the nature of the plant. Schimper in making his constructions overlooked the fact that, because a circle can be described by turning a radius round one of its extremities, it does not follow that circular surfaces in nature must really have been formed in this way; in other words, he did not see that the geometrical consideration of arrangements in space, useful as it may otherwise be, gives no account of the causes to which they are due. But this was not properly an oversight in Schimper's case, for he would have scarcely admitted efficient causes in the true scientific sense into his explanations of the form of plants. How far Schimper was from regarding plants as something coming into being in time and according to natural laws, how profoundly he despised the principles of modern natural science is shown in his judgment of Darwin's theory of descent and of the modern atomic theory, the coarseness of which is the more surprising, because Schimper was a man of refined and even poetic feeling. 'Darwin's doctrine of breeding,' he says, 'is, as I discovered at once and could not help perceiving more and more after repeated and careful perusal, the most shortsighted possible, most stupidly mean and brutal, much more paltry even than that of the tesselated atoms with which a modern buffoon and hired forger has tried to entertain us.' Here is the old platonic view of nature flying at modern science; the sternest 'opposites' that culture has ever produced.

The theory of Schimper, which should rather be called the theory of Schimper and Braun, considering the active part which Braun took from the first in framing and applying it, was capable of further development only in the mathematical and formal direction, as was shown especially in Naumann's essay, 'Ueber den Quincunx als Grundgesetz der Blattstellung vieler Pflanzen' (1845). The defects above described, but not the merits of the theory were shared by the doctrine of phyllotaxis laid down about ten years later by the brothers Louis and Auguste Bravais. Their theory makes use of mathematical formulae to even a greater extent than that of Schimper without paying any attention to genetic conditions, and yet it is less consistent with itself, for it assumes two thoroughly different kinds of phyllotaxis, the positions in which are arranged in a straight and in a curved line; for the latter without any apparent reason a purely ideal original divergence is assumed which stands in irrational relation to the circumference of the stem, and from it all other divergences should be derivable; and this ultimately degenerates into mere playing with figures which in this form afford no deeper insight into the causes of the relations of position. As regards serviceableness in the methodic description of plants the theory of the brothers Bravais is much inferior to that of Schimper^[8].

The genetic morphology founded about the year 1840 had to make the best terms it could with the doctrine of phyllotaxis, which was constructed on a totally different principle; the two went their way on the whole side by side without disturbance from one another till the year 1868, when Hofmeister in his general morphology attacked the principle of Schimper's theory, and endeavoured to substitute a genetic and mechanical explanation of the relative positions for the purely formal account of them; this attempt however, which from the nature of the case has not yet led to a finished theory but nevertheless contains the germ of a further development of this important doctrine, does not come within the scope of this history.

The doctrine of phyllotaxis of Schimper and Braun, as it appeared after 1830, had clearly presented only one side of the theory of metamorphosis; what other elements there were in it capable of being turned to speculative account were further cultivated by Alexander Braun between the years 1840 and 1860. In this period fresh points of view were asserting themselves in botanical research; the founding of the doctrine of cells, the study of the more delicate anatomy of plants and of the history of development, and increased methodical knowledge of the Cryptogams were enlarging the repertory of botanical facts, while the physico-mechanical method of investigation was being more and more adopted. Braun, who took an active part by his own researches in this revolution in morphological botany, remained true nevertheless to idealistic views; and in his frequent and comprehensive discussions of the general results of the new investigations in accordance with these views he has shown how far the idealistic platonising contemplation of nature is in a condition to do justice to the results of exact inductive enquiry. The opposition between his point of view and that of the most eminent representatives of the inductive method became more and more pronounced as years went on, and must be treated here as a historical fact. But if the new tendency in botany pursued especially by von Mohl, Schleiden, Nägeli, Unger, and Hofmeister may be called inductive in the absence of a better term, and be contrasted with the idealistic tendency represented by Braun and his school, it must not be supposed that the latter did not equally contribute in matters of detail to the enriching of the science by the method of induction; on the contrary, Braun himself was the author of a series of important works conceived in this spirit. When the new method is here called inductive, it should be understood that the word is used in a higher than the usual sense, and some explanation of this point will not be superfluous in this place. Idealistic views of nature of all times, whether they present themselves as Platonism, Aristotelian logic, Scholasticism or modern Idealism, have all of them this in common, that they regard the highest knowledge attainable by man as something already won and established; the highest axioms, the most comprehensive truths are supposed to be already known, and the task of inductive enquiry is essentially that of verifying them; the results of observation serve to elucidate already received views, to illustrate already known truths; inductive enquiry has only to establish individual facts. But in the sense in which inductive enquiry was understood by Bacon, Locke, Hume, Kant, and Lange, its task is one that goes essentially farther than this; it must not be content with establishing individual facts, but it must employ them in the critical examination of the most general notions that have come down to us, and do its best to deduce new and comprehensive theories from them, even where these may be entirely opposed to traditional views. But it is part of the very nature of this method of investigation, that its general results are subject to constant modification and improvement; each more general truth has only a temporary value, and endures as long as no new facts militate against it. The distinction therefore between idealism and the inductive method in the domain of natural science comes to this, that the former fits new facts into a scheme of old conceptions, the latter deduces new conceptions from new facts; the one is in its nature dogmatic and intolerant, the other eminently critical; the one is conservative, the other always pressing forwards; the one inclines to philosophic contemplation, the other to vigorous and productive investigation. To this must be added one point of great importance; the idealistic view of nature, rejecting causality, explains nature from notions of design, and is teleological; ethical and even theological elements are thus introduced into natural science.

It is in this form that the distinction between the idealistic view represented by Braun and the modern inductive morphology presents itself to us. If it were the task of this history only to record the discovery of new facts, it would be superfluous to allude to these differences here; but then it would also be impossible to estimate rightly that portion of Braun's long scientific labours which is at once the most original and the most interesting from the historical point of view, and which is to be found not so much in his many descriptive and monographic works, as in his philosophic efforts in the domain of morphology; these moreover deserve our consideration, because they carry out Goethe's half-explained conceptions to their remotest consequences, and express in purer form the idealism which lies at the foundation of the older nature-philosophy. No botanist since Cesalpino has so thoroughly endeavoured to leaven the entire results of inductive investigation with the principles of an idealistic philosophy, and to explain them in its light. Braun's philosophical views not only accompany his knowledge of facts, but everywhere permeate and colour it; in his writings, contributions, and monographs on the most various subjects, facts are regarded from the point of view of his philosophy. He has given a general view of his philosophical principles and illustrated them by a vast variety of facts in his famous book, 'Betrachtungen über die Erscheinung der Verjüngung in der Natur, insbesondere in der Lebens- und Bildungsgeschichte der Pflanze' (1849-50). He himself directs attention to the opposition between his own stand-point and the modern induction in the tenth page of the preface, where he replies to the obvious objection, that his ideas may be regarded as antiquated, in the words, 'A more living contemplation of nature, such as is here attempted, which seeks in natural bodies not merely the operation of dead forces, but the expression of a living fact, does not lead, as is supposed, to airy structures of fancy, for it does not pretend to gain a knowledge of life in nature in any other way than as it is revealed in phenomena,' etc. This thought is still more distinctly uttered in page 13 of the text; 'As external nature without mankind presents to us only the spectacle of a labyrinth without a guide, so too scientific contemplation, which denies the inner spiritual principle in nature and the intimate connection of nature with the informing spirit^[9], leads to a chaos of substances and forces, which are unknown because divorced from spirit, or, to speak more precisely, to a chaos of nothing but unknown causes, which work together in an inexplicable manner.' In a note to this passage he points expressly to 'the comfortless character of such an unreal mode of viewing nature, which must necessarily endeavour to root out everything in the conceptions and language of science which appears from its own point of view to be anthropopathic,' and he requires a tender, ethical element as essential to botanical investigation. The chief object of the volume is to prove that everything in organic life may be resolved into rejuvenescence, of which idea no definition is actually given, though the whole contents of the book are a search after a definition. We may regard the idea of rejuvenescence, as presented by Braun, as an extension of the idea of metamorphosis, in which extended form it is adapted to take in even the results of the cell-theory, of the history of development, and of the modern knowledge of the Cryptogams from the idealistic point of view. One peculiarity of his mode of expounding his views is observed here, as on other occasions, namely, that he gives no precise and arbitrary definition to a word, for instance, like rejuvenescence in the present place, and in a later work to the word individual, but looks behind the word for a profound or even mysterious meaning, which is to be perceived and brought to light by contemplation of the phenomena. In page 5 he says, 'Thus we see youth and age appear alternately in one and the same history of development; we see youth burst through age, and by growth or transformation step into the middle of the development. This is the phenomenon of rejuvenescence, which is repeated in endless multiplicity in every province of life, but nowhere appears more clearly expressed or more accessible to investigation than in the vegetable kingdom. Without rejuvenescence there is no history of development.'—'If then we ask for the causes of the phenomena of rejuvenescence (page 7), we shall indeed allow that nature, into which special life enters in its various manifestations, excites, awakes, and works by the influences which the years and even the days bring with them; but the true and inner cause can only be found in the desire after perfection which belongs to every being in its kind, and urges it to bring the outer world, which is strange to it, more and more into complete subjection to itself, and to fashion itself in it as independently as its specific nature admits.' Further on he says (page 17), 'The impulse or tendency to development in each creature is likewise no direction of activity impressed from without, but one given from within and working as an inner determination and force from the depth of the inner nature.' A passage also from page 111 of his treatise on polyembryony, published in 1860, may be quoted here; 'Though the organism, in the process of realising itself, is subject to physical conditions, yet the proper causes of its morphological and biological characteristics do not lie in these conditions; its laws belong to a higher stage of development of its being, to a sphere in which the faculty of self-determination is distinctly manifested. If this is so, the laws of an organic being appear as tasks imposed, the fulfilling of which is not absolutely necessary but only in relation to the attainment of a definite end, as precepts, to which strict obedience may possibly not be paid.' To return once more to the idea of rejuvenescence, we find at page 18 the words, 'As regards the idea of rejuvenescence, from the foregoing considerations we draw the conclusion, that the surrender of growths already accomplished and the going back to new beginnings, the commencement of rejuvenescence, indicate only the outer side of the proceeding, while the essential part of it is an inner gathering up of forces, a new creating, as it were, out of the individual principle of life, a fresh reflecting upon the specific task or the gaining renewed hold upon the type which is to be presented in the outer organism. By this means rejuvenescence maintains its fixed relation to development, which can and ought to present in gradually attained perfection that only which lies in the nature of the creature, and is most intimately its own.' And at the conclusion of the work (page 347) he says, 'The way in which the inner spiritual nature of life is specially manifested in the phenomenon of rejuvenescence may be defined as reminiscence in the true sense of the word, as the power of grasping anew in the phenomenon the inner destination of life as contrasted with its daily alienation and decay, and applying it with renewed strength towards that which is without,' etc.

This conception of rejuvenescence is, then, applied to all the phenomena of life in plants; not only the metamorphosis of leaves, the formation of shoots and their ramification, and the different modes of cell-formation, but even palaeontological facts are manifestations of rejuvenescence, which in the sequel puts off the form of an abstract idea, and becomes personified into an active personality, as is seen in page 8 in the expression, 'activity of rejuvenescence.'

The relation of Braun's views to the question of the constancy of species may to some extent appear doubtful; some utterances of his may be interpreted to admit a transmutation of species accomplished in the course of ages, while others are opposed to this, and it is the latter which appear to be consistent with the idealistic position. We read, for instance, at page 9, 'The appearance, as though the like was always repeating itself in nature, is suggested when we glance back from our station in time upon the succession of former epochs. Here we find the real first beginnings of species and genera, and even of orders and classes in the vegetable and animal kingdoms; we see at the same time that more or less thorough transformations are connected with the appearance of the higher grades in the organic kingdom, so that genera and species of the old world disappear, and new ones step into their place. All this change expresses not the mere accident of convulsions, which, while they destroy, at the same time prepare new ground for the prosperity of organic nature, but rather definite laws whose action pervades all the individual detail of the development of organic life.' On the other hand we find at the conclusion of the treatise on polyembryony, written a short time before the appearance of Darwin's memorable work, a sentence which makes the assumption of a transmutation of species appear very doubtful; it says (page 257), 'If we are justified in assuming a general organic connection in the history of development in plant-forms, can we imagine that the type of the Mosses and of the Ferns has come from the Algae, or vice versa, that the Alga-form owes its origin to the Mosses and Ferns?'

The sentences here quoted to show Braun's philosophical position still give no idea of the way in which the principles embodied in them influence the whole manner of presenting the facts in the arrangement of his empirical material, but to give a clear idea of this is impossible in so brief a notice as the present. His conception of his subject is shown still more distinctly in a treatise which appeared three years later, entitled 'Das Individuum der Pflanze in seinem Verhältniss zur Species, Generationsfolge, Generationswechsel und Generationstheilung der Pflanze' (1852-3). The definition of the word individual is here sought, as that of rejuvenescence was in the previous work,—a really difficult task, if we consider how many meanings have been assigned to this word in the course of time; in the individuals or atoms of Epicurus, the individuals or monads of Leibnitz, the atoms of modern chemistry, the speculations of the schoolmen on the 'principium individuationis' as opposed to the reality which they assigned to universal conceptions, and in the customary application of the word in every-day language, in which a man or a single tree is called an individual, we have the general views of various centuries, showing how the sense and meaning of old words become changed, not unfrequently into their exact opposites. From the nominalist position of modern natural science this is of little importance, because this treats words and ideas as mere instruments for mutual understanding, and seeks no meaning in either which has not been previously and purposely assigned to them. Braun's mode of proceeding is quite different; by comparison of very various phenomena of vegetation, and by examining former views on the subject of the individual plant, he seeks to demonstrate a deeper meaning which must be connected with the word.

Moreover, he makes the enquiry into the individual only a thread on which to string his own reflections, in the course of which he once more explains the principles of the teleological nature-philosophy, and points out its opposition to modern science, the latter being grievously misrepresented as materialistic, its atoms qualified as dead, its forces as blind. It would scarcely be guessed from Braun's account that the history of philosophy could point to Bacon, Locke, and Kant, as well as to Aristotle, that even the question of the individual had been already handled by the schoolmen. A consideration of the other point of view would have been all the more profitable, since the author in the beginning of his treatise expresses the opinion that the doctrine of the individual belongs to the elements of botany; it might certainly be maintained that it is altogether superfluous.

His train of thought in search of that which must be called an individual in the vegetable kingdom is briefly as follows: In forming a conception of the plant-individual as the unity of a cycle of formation or a morphological whole, our chief difficulty lies in the division into parts and the divisibility (Getheiltheit und Theilbarkeit) which are present in the very different stages of the organic structure of plants. It is requisite therefore to find the middle way between the morphological consideration of the individual plant which breaks up the whole from above downwards, and the physiological which extends it in the upward direction beyond all limits. Neither the leaf-bearing shoots, though they are capable of developing into independent plants, nor the parts of them, which have the same power, neither the single cells, nor the granules they contain, and least of all the atoms of dead matter which are the sport of blind forces, would answer to the idea of the individual in plants. We have therefore to decide which member of this many-graded series of potences in the cycle of development subordinated to the species deserves by preference the name of individual (p. 48). A compromise is then made; it is sufficient to find a part of the plant which answers above all others to the idea of the individual, for in this idea there must be two genetic forces, multiplicity and unity. He then decides for the shoot or bud. 'In contemplating the plant-stem which is usually branched, especially a tree with its many branches, mere instinctive feeling awakens the suspicion that it is not a single being, a single life, to be classed with the individual animal or individual man, but that it is a world of united individuals which spring from one another in a succession of generations,' etc. He proceeds to show that this conception, arising as it does from a sound, natural feeling, is also confirmed by scientific examination. It appears, however, that many phenomena in the growth of plants will not fall in well with this instinctive feeling, and so he says at page 69, 'We cut the Gordian knot in this way, that if we have other and sufficient grounds for regarding branches as individuals, we come to the determination to let every branch pass for an individual, however strongly the appearance may be against it.' The shoot is therefore the morphological individual in the plant, and is analogous to the individual animal. It may certainly be objected, that we may cut the knot in another way and maintain with Schleiden that the cells are the individuals in the vegetable kingdom, if we do not actually arrive by the same path at calling each atom, or at the other end of the scale the whole self-nourishing plant, an individual, for about equally strong reasons might be adduced for both one and the other of these views. It all depends on the point of view we adopt in such speculations, and on the weight we allow to instinctive feeling in establishing scientific ideas. Braun declares very decidedly in page 39 against the notion that the invisible 'individua' or atoms of dead matter can be introduced into the consideration of the plant-individual, as though the plant were a mere concrete of mutually attracting and repelling atoms. If, he says, we will understand by the term individual something absolutely indivisible, this is certainly the last resort, but then we shall have no plant-individual. Moreover, no eye has ever seen these atoms; their assumption is a mere hypothesis, which we may confront with the other hypothesis of the continuity and permeability of matter. The question therefore, he says, at page 39, is whether we can speak of individuals in plants at all, and this coincides with the other question, whether the plant is a mere product of the activity of matter, and so an unsubstantial appearance in the general circulation of nature, the offspring of blind agencies, or whether it possesses a peculiar and independent existence. The views of the physiologists, who reject the vital force and explain the phenomena of life by physical and chemical laws, have robbed life of its mysterious and most directly operative principle, and pulled down the strong wall of separation between organic and inorganic nature. 'Because physical forces appear to be everywhere confined to matter and show in their operation a strict subjection to law, men have ventured to regard the sum total of natural phenomena as the result of original matter working in conjunction with definite powers according to the laws of blind necessity, as a natural mechanism moving in endless circulation.' But he objects that the eternally necessary can only be conceived of as accomplished from all eternity, and thus this physical view would make all eventuality inconceivable. Further, the purpose of the movement of nature must remain an insoluble enigma in this scheme of blind necessity. 'The inadequateness of the so-called physical view of nature as compared with the teleological is therefore most felt in the domain of organic nature, where special purpose in the phenomena of life appears everywhere in greatest distinctness.' The last remark is indisputable so long as we maintain either the constancy of species or a merely internal law of development; the solution of the enigma was discovered a few years later in Darwin's hypothesis, that all adaptations of organisms are to be explained by the maintenance or suppression of varieties, according as they are well or ill provided with the means of sustaining the struggle for existence. No other refutation or rather explanation of teleology in the science of organic life has hitherto been attempted. It has been already pointed out that systematic botany, by establishing the fact of affinity, saw itself compelled at last to give up the constancy of specific forms in order to make this fact intelligible, and here we see how the idea of the adaptation of organisms is found to conflict with causality, unless we assume that the forms which arise through variation only maintain themselves, if they are sufficiently adapted to the surrounding conditions. The movement which began with Goethe and the nature-philosophy assumed a clearer form, found its purest expression, and revealed its most hidden treasures in the writings of Schimper and Alexander Braun; it would be superfluous to submit to a detailed review the numerous works of less important representatives of these views.

We turn from this realm of idealistic philosophy and imagination, from rejuvenescence, the wave-pulse of metamorphosis, the spiral tendency of growth, and the individuality of plants, to the last chapter of our history of systematic botany and morphology, where there is less dogmatism and less poetry, but a firmer ground on which will spring an unexpected wealth of new discoveries and of deeper insight into the nature of the vegetable world.

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1. See Wigand, 'Geschichte und Kritik der Metamorphose,' Leipzig, 1846, p. 38.
2. See Goethe's collected works in forty volumes, Cotta, 1858, vol. xxxvi.
3. See Haeckel, ' Natürliche Schöpfungsgeschichte,' ed. 4, 1873, p. 80.
4. Robert du Petit-Thouars was born in Anjou in 1758 and collected plants during many years in the Mauritius, Madagascar, and Bourbon. He was afterwards Director of the Botanic Garden at Roule, and became Member of the Academy in 1820. He died in 1831. His articles in the 'Biographie Universelle' prove him to have been a writer of ability. Preconceived opinions interfered with the success of his own investigations, especially into the increase in thickness of woody stems, and obstinate adherence to such notions prevented an unbiassed interpretation of what he saw. See Flora, 1845, p. 439.
5. K. F. Schimper, born in Mannheim in 1803, was at first a student of theology in Heidelberg, but having afterwards travelled as a paid collector of plants in the south of France, he applied himself to the study of medicine. From 1828 to 1842 he was employed as a teacher in the University of Munich, though occasionally engaged in exploring the Alps, Pyrenees, and other districts, in the service of the King of Bavaria. It was during this period of his life that he composed his most important works on phyllotaxis, and essays on the former extension of glaciers, and on the glacial period. He returned to the Palatinate in 1842, and died at Schwetzingen in 1867 in the enjoyment of a pension from the Grand duke of Baden.
6. See Hofmeister, 'Allgemeine Morphologie' (1868), pp. 471, 479, and Sachs, 'Lehrbuch der Botanik,' ed. 4 (1874), p. 195.
7. See Nägeli, 'Beitrage zur Wissenschaftlichen Botanik' (1858), I, pp. 40, 49.
8. A comparison of the two theories and a refutation of Schleiden's assertion, that that of the brothers Bravais expresses better 'the simplicity of the law,' will be found in 'Flora,' 1847, No. 13, from the pen of Sendtner, and in Braun's 'Verjüngung,' p. 126.
9. This is not at all true of modern inductive science, which merely forms a different idea of the connection, and has regard to the relation between the percipient subject and the phenomena.