The Life of the Plant

1 Several botanists (Korjinsky and Famintzin in Russia) have recently- advocated the theory of the psychical activity of plants. I would only So, then, neither in the life of the animal nor in that of the plant have we found a single feature specially peculiar to the one or to the other ; not a single indica- tion by means of which any and every organism might be classified In the one or the other kingdom. Is there then no difference between plants and animals ?

The difference is, in truth, very apparent ; it is too deeply rooted in our minds to be given up so easily. Common sense based upon everyday experience persists in repeating, whatever we may say, that a tree will always be a tree and a horse a horse, that a whole abyss lies between them. How can we reconcile this contradiction ? Some- times the difference is plain, sometimes it is not. The issue is simple and the contradiction comprehensible. It is based upon a logical fallacy, on the strength of which man attributes real existence to abstract ideas, the creations of his own mind. Unfortunately this fallacy is very widespread, and has not a little thwarted the success of natural science. As a matter of fact there are no plants or animals as such, but a single undivided world. Plants and animals are only aver- ages, typical conceptions that we form for ourselves, attributing special significance to some properties, and neglecting, almost ignoring, the rest. These con- ceptions, moreover, were formed at a time when only the outstanding representatives of these groups were known. So long as the comparison dealt with a tree and a horse, no misunderstanding was possible ; but the matter appeared in quite a different light when

point out that this theory has not brought forward a single argument based upon fact. Only metaphysical, not scientific, considerations can be adduced in its defence to-day, just as a quarter of a century ago when I first raised the question. I would also remark that to explain com- paratively simple phenomena of vegetable life by comparing them with much more complicated phenomena of psychical life in animals is to leave the track by which every science, every kind of knowledge, has advanced until now.

all living beings had to be taken into consideration as a whole. Then the unity of the organic world had to be admitted, and the realisation dawned that all our divisions are only the production of our own mind. I agree that the former conception was among the greatest acquired by the human mind ; it would have been quite impossible to master without it the chaos of individual forms. We must not lose sight, however, of the real value of the logical method we are using ; we must not identify types and abstract ideas with real existences.

Granting, however, that such a dualism does not exist in the organic world, that instead of considering plants and animals as two absolutely different categories of beings we are to realise them only as two typical concep- tions, nevertheless once our mind has formed these two conceptions we must do our best to describe them, pointing out the peculiarities to which we give prefer- ence, and which of them we connect with the conception of a plant.

I do not think we can offer to-day any shorter and more appropriate definition than that expressed in the old saying, that ‘ a plant grows, but is deprived of voluntary movement.’ Let us try to discover a more definite meaning for this saying. The movement of an animal, as indeed any kind of motion, is governed by general mechanical laws. The peculiarity of the animal consists in the fact that the centre of the forces acting upon it lies within itself, hence its independence of external conditions. The source of these forces is con- cealed in the process of oxidation. This takes place all over the body, manifests itself in respiration, and becomes the source of the heat and motion, which, on the whole, characterise the animal in contradistinction to the plant. I say 1 on the whole,’ because we have only just found ample proof that these processes are also met with in plants ; but there they recede into the

background, because completely screened by other pre- dominant processes. We have already seen 1 that under the action of light the green parts of the plant manifest a phenomenon exactly opposite to that of oxidation, i.e . the decomposition of carbonic acid, accompanied by the accumulation of carbon. This process is almost twenty times as energetic as the respiration of plants, so that, for instance, to one pound of carbon burning down in a plant, twenty pounds of it are formed : the plant uses for its requirements only one-twentieth of all the carbon deposited in it, hence the accumulation of matter, the enormous increase in mass, that startles us in the phenomena of growth . Whereas, in the case of animals at the stage of full development, a certain balance becomes established between gain and loss of matter ; in the case of plants, growth, i.e . accumulation of matter, takes place almost as long as they live. 2 However, this accumulation of matter depends entirely upon the sun ; hence the utter dependence of plants upon external conditions, and the passivity which so sharply differentiates them from the independent activity of animals.

It follows that the difference between plants and animals is not qualitative, but only quantitative. The same processes take place in both kingdoms, but some of them predominate in the one and some in the other. If in the end we have oxidation, waste of matter and manifestation of energy, we have before us , the type of an animal ; if, on the other hand, we have deoxidation, accumulation of matter, absorption of energy, we have the type of a plant. Plants and animals have divided labour between them. Animals use up the matter and

a This comparison is, however, not quite accurate. It is more accurate to consider as the individual in a plant a separate shoot which has a limited growth, rather than the whole plant, which, like a tree for instance, presents a complicated organism. It grows like a coral for an indefinite length of time. energy stored by plants ; plants in their turn derive the energy they require from the sun. Animals depend on plants and plants depend on the sun.

We arrive in this way at the most general conception of the life of the plant, at the realisation of its principal function, the part it plays in the organic world. It plays the part of mediator between the sun and the animal world. The plant — or rather, its most typical organ, the chloroplast — is the link which unites the activity of the whole organic world, all that we call life, to the centre of energy in our solar system. Such is the cosmical function of the plant.

When the type of a green oak rises before our imagina- tion, rustling its luxuriant foliage in summer, bare and frozen in winter, enduring all the fluctuations of the external temperature ; when we think of that oak year after year, century after century increasing in organic mass, yet always fixed to the same place, and then look at a Russian trotter flying like an arrow, giving off in winter clouds of vapour, and learn that it uses both in winter and in summer quantities of hay and grain ; when we subsequently learn that these opposite external phenomena are only the necessary results of the chemical processes which predominate in the one or the other case ; then the antithesis between plants and animals stands out clearly before us. But when we venture to cast a general glance not only upon these typical representatives, but upon all plants and animals and upon the whole of their functions, we are compelled to realise the inadequacy of such an antithesis. This contradiction vanishes, and everything becomes comprehensible the moment we ad- mit that the stream of organic life, working its course in the beginning along a single bed, has subsequently divided into two branches ; so that now, standing at their mouth, we seem to see two independent currents. It is only when we try to follow both currents along their entire course till we rise to their common source

that we come to the conclusion that they are only two branches of one and the same potent stream of life. With this we sum up the survey of the vital functions of the plant. We have studied the structure of its different organs, have learnt their significance, and have thus solved a twofold problem, which is always facing the physiologist : given an organ, to find its function ; given a function, to find an organ corresponding to it. We have observed how perfectly every single organ fulfils its function, how well it is adapted to its environ- ment, how indispensable is the reciprocal activity of different organs, and how harmoniously they work together in the general life of the plant ; how remarkable is the co-operation of certain organisms, though belong- ing to different kingdoms of the organic world ; how harmonious is the reciprocal activity of these two kingdoms taken together. The study of all these facts seems to justify us in saying we have reached the end of our course. But it is precisely here, at this apparent limit, that the physiologist begins to realise, though faintly, that his subject is not exhausted, that beyond all these particular problems there arises the most general and universal inquiry : Why is it that all these organs, all these beings are so perfect, so wonderfully adapted to their environment and functions ? The more striking the fact, the more perfect the organism, the more haunting is the question : Why is it so perfect ? By what means has it reached this perfection ? Is it worth while to go through such a long course in order to hear at the end the laconic answer : I do not know, nor understand, nor shall ever understand. It is true that a naturalist is liable to say this, is even more liable with sincerity to give this answer than any other investigator; but, at the same time, he most willingly grasps the first opportunity for an explanation,

most jealously defends those provinces of knowledge into which faint rays of light have succeeded in penetrating. The degree to which science is able to satisfy, in the present case, the natural curiosity of the human mind, and offer a key to what has been considered as the essential feature of the organic world — its perfection, harmony, or teleological finality 3 — will be studied in our next chapter. We came to the conclusion in our last chapter that every thinking man, who turns his attention to the phenomena of organic Nature, and still more so the naturalist, who studies them more thoroughly, becomes convinced that the organic world as a whole, as also in its several parts, is marked by one common char- acteristic which we try to express by the words perfection, harmony, etc. This conviction in its turn is succeeded by the involuntary desire, the irresistible demand for an explanation of this most salient feature of living beings. Formerly, on reaching this stage in his investigations of Nature, the naturalist considered his course had come to an end. He accepted this fact of the perfection and harmony as a primary, an elemen- tary phenomenon, beyond the reach of further scientific analysis ; and according to the particular turn of his mind he either fell into silence, or gave vent to enthusiastic effusions on this gratifying theme. But besides this preponderating opinion some courageous pioneers in the domain of science ever and anon gave voice to the demand that this general characteristic of organic forms should be treated in the same way as particular phenomena, i.e. that, not satisfied with the simple statement of the fact, science should try to explain it in a more rational way, should treat it as a particular case depending upon other more general laws ; that, not resting satisfied with the empirical knowledge that such is the case, science should strive towards the deductive conclusion, that such must be the case. What can

these general laws ultimately be if, starting with them, we arrive as a necessary conclusion at the startling perfection of the organic world ? We shall devote this our last chapter to answering this question. Hitherto, whenever we have undertaken to explain particular phenomena of vegetable life, we have always tried to explain them by more general and compre- hensive physical and chemical laws. In the majority of cases we have succeeded more or less fully, without even once having had recourse to the mysterious vital force of which such lavish application was made by earlier physiologists. We have not proved the inade- quacy of this said vital force with its indefinite attri- butes and intangible sphere of action ; we have not even ventured to refute its very existence ; we have simply not found room for it in our lectures — and we have never had cause to regret it.

But now the question arises : Can this method of explanation be applied to all the facts of vegetable life ? Are we able, for instance, to explain by means of physical forces alone the origin of the remarkable and perfectly adapted forms which we studied especially in our last two chapters ? Can we, for instance, by any possible combination of physical forces at work at the present moment, explain the formation of the flower of the sage plant, so wonderfully adapted in all its details to the co-operation of insects in the process of cross- fertilisation so beneficial to the plant ? Or can we by the same means explain why the leaves of the catchfly or the sundew possess all the necessary mechanical and chemical properties for making them perfect implements for catching and devouring insects ? Apparently not. Evidently all these forms, or rather their expediency, cannot in the least be accounted for as a necessary outcome of the interaction of the sub- stances and forces under the influence of which the organism investigated has been formed. But if we

cannot account for these forms by starting from the conditions of their individual existence, can we not find the desired explanation by some other method ? When a historian or a politician studies the life of a nation, and at a certain period of its existence comes across a certain phenomenon which is not the direct result of the morals and customs eurrent at that particular time, nor of the contemporary conditions of life, or when he finds a very perfect and fully organised form of govern- ment or society, he has recourse to historical causes in order to explain them. Failing to find a ready answer in the present, he looks for it back into the past. Are we not entitled to use the same method for explaining pheno- mena in Nature ? When an organ appears extremely well adapted to its function, when we see an organism in full harmony with its environment, and yet feel that the contemporary influences at work upon the individual organism are inadequate to explain its origin, are we not then entitled to assume that this perfection did not arise suddenly, but has been accomplished by a slow process of historical development, and that in this way the adaptation has been in the long run wrought by the same physical forces as are at work at the present time ? Are we not entitled to assume that physical forces which may be unable to affect so deeply a single organism are yet able to cause a distinct change in the course of a long series of generations ?

In order to admit such an interpretation of Nature, we must begin by proving two propositions : firstly, that the organic world has its history; and secondly, that this historical process inevitably and infallibly leads to perfection. If we succeed in proving the truth of these statements, we shall obviously have found the general key to the explanation of the per- fection of organic forms. frequently answered this question in the affirmative, but we have had no occasion as yet to consider the whole body of proof that exists in support of such a state- ment. This proof is given first of all by geology. We have already seen in our first lecture that the vegeta- tion of our planet is not the same to-day as it was in former geological epochs, and that the more remote is the epoch investigated the simpler are its forms. Waterweeds appear first, then mosses, later still horse-tails, ferns and club-mosses — all spore-plants; eventually seed-plants appear, and of these the conifers come first ; whereas the latest, the most complicated and perfected in their organisation, are the dicotyledons, which to-day predominate on our planet. Thus, in course of time, to types already existing new types of plants have been added which have overcome them in point of numbers ; and, moreover, the simplest have been followed by the more complex. As we have already seen in our first lecture, this funda- mental geological fact can be explained by two con- tradictory hypotheses : either the new types were formed anew, quite independently from those that existed before them, or they have arisen from them by means of transformation, and therefore are directly re- lated to them. I call both of these theories hypotheses, and we cannot repeat it too often, because the exponents of the first theory have applied this term with re- markable persistence and assurance to the second theory alone, forgetting that the one they hold is as much a hypothesis as the other ; that it is an arbitrary interpretation and not a simple statement of fact.

Let us try to estimate the relative merit of these two hypotheses. Let us see which of them agrees the better with reality, explains the greater number of facts, meets fewer contradictions — in a word, satisfies the better the conditions we have to require of every scientific hypothesis. The idea that one plant may have arisen from another, an oak from a birch, a rose from a lily, appears so strange at first, that the mind cannot easily grasp it. But is it easier to realise that a cotyledon, a petal, a stamen, a pistil have arisen from a leaf, so dissimilar to them all ? And yet when we discussed the theory of meta- morphosis in our first chapter, we were driven to the conclusion that all these organs so different in form, structure and function, are nevertheless merely the outcome of the transformation of a single organ, the leaf. We arrived at this conclusion on the strength of the following considerations. Firstly, on the ground of the existence of insensible transitions : e.g. we have seen a series of organs in the water lily, neither petals, nor stamens, but similar to both, so that it is quite impossible to say where the one ends and the other begins. The second consideration in favour of the gradual transformation of organs is based upon the monstrosities to be found in plants, ix. cases in which one organ accidentally acquires the form of another, e.g . when the pistil of a peony assumes the shape of a red petal with ovules at its edges. Cases are most convincing in which such transformation is caused artifi- cially, as for instance in double flowers, where stamens become transformed into additional petals ; as also in experiments, where the outer scales of leaf-buds are transformed into actual leaves. Since these considera- tions force us to admit the possibility of the transforma- tion of one organ into another quite different from it, we are bound to admit more easily still the possibility of such transition between similar organs in different plants.

Once we admit that a stamen has arisen from a leaf, we can admit with greater assurance that the leaf of one plant can arise from the leaf of another ; the flower of one plant from that of another. We are forced to do so on the strength of the very considera- tions just brought forward, i.e . on the strength of the existence of transitional forms and of so-called mon- strosities, i.e. direct transformations. Let us dwell upon some examples. When we were discussing flowers we had an oppor- tunity of studying the sage, a plant used by chemists, and remarkable for its adaptations for cross-fertilisation by means of insects. We will try to demonstrate the existence of gradual stages in the formation of this most interesting flower from an apparently quite different flower, regular and radially symmetrical in form. The sage belongs to the family of Labiate flowers, so called on account of their corolla having in most cases two lips. The wild thyme, mint and other plants also belong to this class. Botanists agree that the Boragineae are in many respects very much like the Labiateae. We may take the forget- me-not as a representative of the Boragineae. Everybody knows that the blue corolla of this flower forms at its base a short tube, and spreads out at the top, dividing into five equal rounded lobes. If we peep into the inside of the tube we notice five similar yellow anthers, with their filaments attached to the tube (fig. 80). 1 Can we admit that the two-lipped flower of the sage with its two peculiar stamens could have descended from this regular star-like flower of forget-me-not with its five stamens ? If we succeed in demonstrating in other representatives of the same two families a series of intermediate forms between the extreme cases we have selected, we shall make this supposition most probable. To begin with, we must point out the fact that among the class of Boragineae, all the flowers are not as regular as the forget-me-not. In the viper’s bugloss, for instance, the corolla already shows signs of bilateral symmetry, i.e. the top and the bottom have

1 Fig. So — 1 shows the corolla of the forget-me-not; 2, of the viper's bugloss ; 3, of the figwort ; 4, of the wild thyme ; 5, of the sage. All the corollae are split along the lower lip and stretched out. The corolla of the sage is also cut along the upper lip. begun to be differentiated, although not so strongly as to form two distinct lips (fig. 80, 2) : at the same time the five stamens are differentiated in size ; the upper one especially (fig. 80, 2 m) is considerably smaller than the others. On the other hand not all Labiate flowers have a distinctly two-lipped corolla ; e.g. mint, where the flowers are almost regular. Consequently,

the transition from a regular to a two-lipped corolla might have occurred gradually. Let us pass to the stamens. The Boragineae have five, the Labiatae four, stamens, of which the two lower are larger and the two upper are smaller (fig. 80, 4, n, n ) . What has become of the fifth ? Whenever an organism lacks an organ, the existence of which can be deduced by analogy with other organisms, we generally find that one of two changes has taken place : the organ has either transformed itself into another organ, undergone a

metamorphosis, or else has entirely disappeared, be- come atrophied, and other organs developed instead. The fact of such compensation, or correlation, in the development of parts was observed by Goethe, to whom, as we know, science owes its theory of meta- morphosis. If one stamen, namely the upper one, disappears in Labiate flowers (the very same stamen which in the viper’s bugloss is already much smaller than others, fig. 80, 2 m), what arises in its place ? We notice that the disappearance of this stamen coincides with the strong development of the upper lip, and hence we may suppose that the stamen has trans- formed itself into the petaloid organ, which joins the two upper petals and forms the upper lip. This need not puzzle us, because the transformation of the stamen into a petal and the fusion of parts in a flower is a very common phenomenon. This can also be proved by the fact that in mint, where the bilabiate corolla is very feebly developed, a fifth stamen is not seldom preserved. An example taken from among other plants will make this inference still more con- clusive. Two other families, the so-called Solanaceae (e.g. potato) and the Scrophulariaceae (e.g. red-rattle, foxglove, etc.,) are correlated in exactly the same way as the Boragineae and Labiatae. The Solanaceae have a regular flower and five stamens ; the Scrophulariaceae have a two-lipped flower and four stamens. How- ever here, and especially in the figwort, we become quite convinced that the uppermost fifth stamen has been transformed into a petal, and has fused with the two upper petals (fig. 80, 3 m).

We can, therefore, explain how the regular flower of the forget-me-not with five stamens could gradually have become transformed into a two-lipped flower with only four stamens, characteristic of the majority of the Labiatae. The sage has only two stamens. Let us follow the fate of the other two. By examining the tube of the corolla of this plant, splitting it longi- tudinally, we find, a little above the two developed stamens — exactly at the spots occupied by smaller stamens in other Labiatae — two scarcely visible atro- phied stamens (fig. 69, fig. 80, 5 n , n). x\ccording to Goethe's theory, mentioned earlier, the remaining two stamens have attained their greater size at the expense of the undeveloped ones, and have thus acquired the peculiar structure already familiar to us (fig. 69) . This peculiarity in the form of the two stamens presents in its turn different degrees of complication in different species of sage, which proves that it did not arise suddenly but by a series of gradual changes. The description of these transitional forms would, however, require too much time as well as too many diagrams 1 * * to be dwelt upon here. We might have made clear by exactly similar arguments how another still more curious flower — the orchid — could have arisen from a regular flower such as the lily. Morphology or the 4 Comparative Anatomy f of plants is full of such examples ; we may say it entirely consists of them.

Thus, if the theory of metamorphosis explains how, by means of a range of insensible transitions, different organs of one and the same plant have been derived from each other, the anatomical study of similar organs in different plants brings us to the similar conclusion, that one vegetable form could have been derived from 1 We came to the conclusion in discussing the flower, that the whole function of this complicated staminal apparatus consists in the promotion

of cross-fertilisation by means of insects. This cross-fertilisation would evidently be more perfectly achieved were the flowers differentiated in sex, i.e. if some flowers contained pistils and others stamens. In this case this complicated and gradually developed staminal apparatus would become useless, and in fact in other species of sage, e.g. in the field sage, in addition to the hermaphrodite flowers female flowers are also found ; in these we are able to observe the way this curious and now useless apparatus gradually became atrophied ; how it has repassed in reverse order through almost all the phases, which it must have passed through, during its evolution.

another ; otherwise, what other meaning can we attri- bute to these rudimentary or rather degenerate organs which meet us at every step, and demonstrate a gradual transition between dissimilar forms ? The study of organisms in the embryonic stage proves this theory still more conclusively. All the data of embryology testify that similarities and homo- logies, which escape attention in fully developed organisms, become comprehensible when the history of their development is studied. Thus, for instance,

the vegetable kingdom than that between spore-plants and seed-plants ; an impassable abyss seems to lie between these two sub-kingdoms, and yet Hofmeister managed to bridge even this gulf. The study of the history of the development of the higher spore-plants and of the lowest seed-plants has revealed the exist- ence of a connexion between these groups, and has even shown the course which this transition must have taken. We have already seen that the most typical

antherozoids, whereas seed-plants are fertilised by means of pollen-tubes. Hofmeister predicted, on the ground of his far-reaching investigations, that inside the pollen-tubes of certain flowering plants anthero- zoids would necessarily be discovered, and twenty years after his death this prediction was actually fulfilled. The exact sciences, such as astronomy, physics, and chemistry, pride themselves upon such predictions. Hofmeister’s prediction is the most brilliant in the domain of morphology . 1 The Gymnosperms, to which our Conifers belong, form a link between the two sub- kingdoms of the vegetable world. It is in some members of this group that antherozoids have been discovered.

1 It is very strange that Prof. Borodine has found it possible not even to mention the name of the great scientist in his detailed work upon this subject {The Process of Fertilisation in the Vegetable Kingdom). But we have already seen that, quite apart from this deduction concerning the history of development, geology had already demonstrated that such was the chronological sequence in the appearance of these groups upon our planet . 1 Let us recall one of the results of the preceding chapter, bearing on the im- possibility of establishing any physiological border line between plants and animals — the fact that the origin of all organisms, the cell, or rather simply a speck of protoplasm, is alike in all living beings, and we shall inevitably admit the unity of the organic world, the relationship, the immediate connexion between all that lives on the earth.

It may seem strange, even incomprehensible, that this conclusion could have met with opposition in the face of such concordant and diverse evidence from all the departments of biology. We do still meet such opposi- tion even to-day. In order to explain the origin of the divergence of view among scientists, we must dwell for a short time upon certain technical and perhaps tedious details, without which, however, the reason for this controversy will remain incomprehensible. An investigator of the organic world very soon arrives at the conclusion that organisms present different degrees of mutual affinity , as it is generally called. In order to express the degrees of affinity in the systematic description of organisms, these are generally associated in groups, and the groups marked by terms which indicate the degree of relation- ship that exists between them ; such are the terms family, genus, etc. The smallest group in which the forms are most similar to each other, the group which represents the collective unit, so to speak,