The Life of the Plant

botanist is a man who spends his life over a microscope, i.e. a man who goes on examining and describing microscopically minute organisms, or else microscopic- ally minute details of large organisms. Although apparently different, the activity of both is essentially analogous : the only difference between them lies in the scale of their operations. While the one observes with the naked eye, the other uses the lens or the microscope ; but both do no more than observe and describe, and the description of a fungus or of a water- weed does not differ from the description of a grass or of a tree. The one and the other forget that the chief object of the scientist is not to describe but to explain and command Nature ; his method must not be that of a passive observer, but rather that of an active experi- menter ; he must engage in strife with Nature, and by the power of his mind extort from her answers to his questions, so that he may master and sub- ordinate her at will, provoke or arrest the phenomena of life, direct or vary them. Of course, among the representatives of the exclusively morphological, or descriptive, tendency there have been powerful minds, who have thrown light upon the mass of accumu- lated material and made it live — a little further on we shall even study an illustration of this — but on the whole their energies have been spent upon conceptions inaccessible to the uninitiated, and therefore they have not been able to excite any general interest. The fine simplicity of some morphological laws, the harmony of natural systems of classification which stand as wonder- ful memorials to the power of the human mind, all this is lost to those who are without the knowledge of the details necessary to the understanding of it.

It is therefore evident that up to the present time botany has been developing mostly along the lines which least interest the public. As we have already seen, the reason lies partly in the historical course of the development of science and partly with botanists themselves. The historical development of every science requires that the more complicated be preceded by the more elementary, and it is obvious that the problems of physiology are much more complicated than those of morphology, and presuppose a greater store of informa- tion. The description of organic forms does not necessi- tate any preliminary knowledge. In order to explain the phenomena of life, on the other hand, i.e. to resolve them into the simplest physical and chemical phenomena — which is, as a matter of fact, the object of physiology — it is necessary to start with some knowledge of these.' phenomena. A morphologist need be but a morpho- logist, whereas a physiologist must to a certain extent be at once a physicist, a chemist, and a morphologist. It was in fact inevitable that the physiological tendency should develop later in the history of science, i.e. only after physics and chemistry had reached a certain point of development. That the backwardness of physiology as a science was nevertheless due in large measure to the onesidedness of botanists themselves is proved by the fact that while the latter were still engaged ex- clusively in the study of form, chemists and physicists were penetrating into the attractive province of the life of the plant and founding the science of plant physiology. The fundamental principles of physiology were therefore formulated by chemists and physicists and not by botanists. The backwardness of botanists in this direction is even more striking when we compare what has been done in the sphere of the physiology of plants with that which has been done in animal physiology.: This may seem somewhat paradoxical : the problem of the physiology of plants is far simpler than that of the physiology of animals.

The life of plants is far less complicated than the life of animals, and yet our know- ledge of the latter is much fuller and more definite. However, there are perhaps some extenuating dreum- stances which may be advanced in the defence of botanists. The progress of the science of animal physiology can be explained by causes lying outside the province of science, by considerations of a practical kind. To develop and prosper, every science requires the moral and material support of society ; but, on the other hand, society takes practical interest only in things which it considers useful. Society has already been convinced of the usefulness of animal physiology, while the idea of the usefulness of the physiology of plants has only just dawned. Almost every science owes its origin to an art of some sort, just as every art in its turn is the outcome of some need in man. This appears to be the inevitable course of the development of human knowledge. To begin with, man appreciates knowledge merely as a means towards obtaining the fullest possible amount of material enjoyment ; only in a later stage does knowledge become to him in itself a source of enjoyment. Intellectual aspirations are then as exacting as material wants. Knowledge considered as a means to an end is art ; knowledge considered as an end in itself is science. Medicine is the art under whose wing the physiology of animals developed. After many unsuccessful efforts to solve its own problems by means of rough empiricism or abstract thought medicine came to the conclusion that it must go further back to study the laws of animal life and join hands with science ; thus it was that the science of animal physiology arose and developed in the medical schools. But, together with the necessity for preserving physical health to which medicine answers, man has other needs ; he requires food, clothing, a roof over his head, and means of locomotion. He obtains the majority of these commodities directly or indirectly from plants which he cultivates and tends. It is only after studying the laws of their existence, after learning by observation or experiment from the plant itself the means by which it

accomplishes its aims, that we are able to direct its en- ergies to our advantage and oblige it to yield us the best and most abundant fruit. Obviously the physiology of plants must be made the foundation of agriculture. Agriculture, like medicine, rambled on for a long time in the sterile provinces of empiricism and speculation before it came to this conclusion. The same thing has happened there as happened in medicine so many years previously. Rational agriculture is a much younger science than rational medicine ; consequently the necessity for a knowledge of the physiology of the plant, and a demand for such knowledge, arose also later. But the necessity having once arisen, it cannot remain without influence upon the fate of the physiology of plants. The physi- ology of plants will develop in the schools of agriculture in the same way as the physiology of animals developed in the schools of medicine. A whole network of ‘ experi- mental stations ’ has already spread over Germany and America ; the Government in France, private individuals and societies in England, are working towards the same end ; even poor Italy, overburdened with debt though she be, is making an effort to pursue the same course.

In all such ‘ stations,’ as well as in other agricultural institutions, experimental physiology has established itself beside agriculture, and is setting to work to further its progress, and gaining at the same time the advantage of the precious experience it has accumulated during so many centuries. So must it be on the analogy of other sciences, and so doubtless it will be. Meanwhile, however, a comparison of these modest experimental stations and the still more modest botanical laboratories of Europe with the luxurious palaces In which medicine dwells, and especially a comparison of the insignificant number of botanists engaged in physiological research with the thousands of doctors who are and have been engaged all over Europe in the study of the physiology

of animals, make patent to every one the fact that this extraordinary number of workers accounts for the appearance of such men as Helmholtz, Claude Bernard, Du Bois-Reymond, and others, beside whom botanical physiologists can as yet cite not a single name. This wealth of equipment, and especially the wealth of mental energy which has been expended upon the subject, has conditioned the success of animal physiology as a science, and may be regarded as an extenuating circumstance for the backwardness of the physiology of plants.

Happily, however, during recent years a fresh aspect of botany has been discovered : life has begun to attract attention which hitherto was exclusively devoted to form. The public has realised at the same time that the physiology of plants tends to an end not merely useful, but even necessary, to society ; that it is served by this science in the same way as by other sciences, which have already gained their civil rights. I must explain myself. I do not wish it to be under- stood from what I have said that I expect science to aspire exclusively to utilitarian ends, as if I found its highest sanction in its practical tendency. On the contrary this practical tendency, which characterises the infancy of a science, cannot and must not be its aim. Throughout the development of a pure science its results find application spontaneously. The develop- ment of a science can be determined only by the logical sequence of its achievements, never by the external pressure of necessity. Scientific thought, like every other form of mental activity, can work only under conditions of absolute liberty. Oppressed by the weight of utilitarian demands, science can produce but pitiable artificial work, after the same kind as any meagre and mechanical work of art fashioned under similar circum- stances. We may ransack the archives of any science and yet find scarcely one daring idea, one brilliant generalisation which owed its origin to its application ;

and, vice versd, history is full of examples of discoveries, which, though unassociated with any practical purpose, have become the source of innumerable practical issues. Now I must summarise this rather lengthy introduc- tion. Comparatively speaking, botany meets with no great amount of sympathy from the public, which interprets it wrongly on the ground of its having pursued objects and been engaged with ideas which could interest but the small class of the initiated. This tendency, caused in the first instance by the inevitable historical development of the sciences, was fostered and is fostered still by the attitude of most botanical scholars. Recently, however, a new and refreshing trend of thought has been observable gradually forcing its way to the front, viz. the trend of thought of experimental physiology. The new awakening of interest is being followed by the realisation of the utility of this science. Agriculture is beginning to demand a knowledge of the physiology of the plant, and in this way the solidarity of interests between science and society is being established. Whereas, however, this community of interests does not on the one hand authorise society to dictate to science its modes of action or the method of its further development, neither has science on the other hand any right to retire as it were into a sanctuary, to conceal itself from the public gaze, expecting its utility to be taken on trust. If the votaries of science wish it to attract the sympathy and support of the public, they must remember that they are the servants of the same public, that occasionally they must step forward as trustees and duly render their account. This is what we have accomplished, they must say ; this is what we are accomplishing, and this is what we are going to accomplish : judge how far our activity has been fruitful, and consequent ly what you may expect in the future.

called popular scientific literature, for popular lectures — a problem often lost sight of because those who set out to treat scientific subjects in a popular way generally devote their attention to but one side of their aim, namely, how they may teach in the easiest and most amusing way. I have said, that in order to understand the life of a plant it is necessary to study its form ; in order to understand the working of a machine a study of its construction is needed. Let us glance at the external, formal manifestations of the life of a plant, the observa- tion of which does not require any preliminary study, nor any technical method of investigation.

Let us begin our sketch with the awakening of the plant’s life after the winter’s slumber. In what state will the spring find it ? Where is hidden the origin of this new life ? It lies concealed in the seed which has maintained its vitality under the shelter of the soil and the thick cover of snow. It is maintained in buds, which have endured the misery of the cold under the protection of their scales. By the action of the warm spring sun every bare piece of ground produces green shoots; on every tree or bush buds swell, burst, and lose their unsightly and already useless scales. The seed and the bud — those are the two organs to which daily experience attributes the origin of the plant’s life. It is therefore with an investigation of them that we shall begin our study.

First, what is a seed and what are its component parts ? Let us investigate the well-known seed of a bean. If soaked in water it will sw r ell and become detached from its skin, or coat. Under the seed-coat we shall find it split into two fleshy or rather hard and cartilaginous parts. In between these will be found inserted a small body connecting them together. With the naked eye, or, better still, with the help of a lens, a small germ plant, a young shoot, consisting of a

tiny stem with leaves and rootlet, ^ x is easily recognised (fig. i). This \ shoot binds together the two iT 0 j halves of the seed, which are I J called the cotyledons. These, y / though much larger than the Fig. i. shoot itself, are nothing but two appendages of it. But what is the nature of these cotyledons? Botanists say they are leaves. Those colourless, round, fleshy bodies, which remain underground are called leaves not without reason, as we shall immediately see. We have only to pass from a bean to its nearest relative — say the haricot — to find cotyledons appearing above the soil and becoming green like ordinary leaves (fig. 2). In the maple and the ash the cotyledons are still more like a common leaf, and the lime actually has small thin green leaves with well- marked veins and crenate outlines. Therefore the cotyledons of a bean, though they grow underground and are far from reminding us of actual leaves by their colouring or appearance, must be nevertheless regarded as such. Following upon those first organs, so unlike leaves, there appear, as the stem elongates, real leaves, though not yet of the shape we are accustomed to meet on a grown-up plant. Here is, for instance, a young ash plant. Everybody knows the shape of its leaf. Several pairs of leaflets are distributed on a common stalk with one leaflet more at the top. In this way a whole leaf consists of seven, nine, or more leaflets. This is called a compound leaf. What, then, do we notice here ? (fig. 3). The two fleshy, tongue-shaped cotyledons are followed by two toothed leaves with prominent venation, which are simple, not compound, leaves. If we look further up the stem we shall notice other leaves composed of three leaflets, higher up

others of five, and lastly of seven or nine leaflets; i.e. here commence leaves like those of which the foliage of a grown-up tree is generally composed. This passage from the cotyledon to the true leaf has happened gradually ; it includes a whole series of intermediate forms. We receive involuntarily from the series the im- pression that one of these organs is formed from the other, and that these are the intermediate stages through which a leaf has to pass.

Let us now consider the bud of a tree, say of a maple, of a horse-chestnut, or of any bush, like that of the currant. We find peculiar organs on the outside of them : dark brown, thin, tough, sometimes sticky and resinous scales. If we pull the bud to pieces or let it open by itself, then tear off its parts one by one and spread them out in a row, we notice the following facts. First in the series are several scales darkly coloured, short, obtuse, almost round in shape (fig. 4). Then

this shape becomes more and more elongated and the colouring passes in- to green ; we notice on the top of one of these scales an indefinite rather crumpled protuber- ance, which further on increases in size and opens out. This protuberance is a real slightly wrinkled little leaf. The deeper within the bud the more clearly this pro- tuberance reveals itself as the part of the leaf which is called the lamina, Fig. 4. while the distended part of the first scales becomes narrower and more elongated, taking the true stem-like form of a petiole (fig. 4, horse- chestnut, and fig. 5, currant bush). This is therefore the same phenomenon as in the young ash : there the cotyledon and here the scale passes into a leaf, through a graded series of intermediate forms. And again the suspicion arises that these are one and the same organ, only modified in appearance according to their special functions.

Having thus started with a seed or with a bud, we have arrived at the typical leaf which makes up all the green foliage of plants. Having produced such a leaf the plant seems to have reached the beaten track and produces one leaf after another, modelling them as it were according to the same pattern, casting them, so to speak, in the same mould. But the leaves are not the only product of a growing plant ; at a certain age it produces other organs such as flowers and fruit. As a rule the transformation of leaves into quite distinct flower organs hap- pens suddenly; but cases are frequent in which the ap- pearance of the flower is anticipated by changes revealed in the upper leaves.

Let us study the well-known garden peony. Everybody knows its leaves (fig. 6). Starting from the lowest and passing up the stem towards the flower we notice that the shape of the leaf changes until it becomes at last almost unrecognisable. At first the whole leaf consists of eleven or nine leaflets distributed in threes. At a certain point we have only three leaflets ; in the interval between these two kinds of leaves we are also likely to find such as have seven and five leaflets. In the end the whole leaf consists of only a single leaflet (fig. 7, left) . The process is the converse of that noticed in the ash. There the shape of the leaf became gradually more complicated, whereas here it becomes less so, passing through the same stages but in the reverse order. So far the simple leaflet has entirely resembled the upper part of the whole leaf, but gradually it also changes its appearance : its short petiole broadens into a flat scale, while the lamina continually decreases until it becomes a small, green, tongue-shaped object on the top

of the scale (fig. 7) ; later still it appears like a small bristle in the topmost hollow of the scale, and at last disappears altogether (fig. 8). We are left with a thin yellowish-green scale, reddish at the edge. Our leaf has gone through its entire transformation before our very eyes, so to speak. Its lamina has disappeared, while its petiole has changed into an organ, similar in origin and purpose to the scale studied in the bud of the chestnut. The one as well as the other represent a petiole, developed like a lamina. As the one protects the young leaves of the bud, so the other protects the

inner delicate parts of the flower. This organ is called * sepal, and the whole whorl of such leaves the calyx. Thus a sepal 1S nothing but a modified leaf. In many thernsJ 13 v u ° bvious ~ as ’ for instance, in the sepal of the rose, which keeps its thin lamina. Very few flowers satin or velvet surface, so vainly imitated in artificial flowers ; these are petals, forming together the corolla.' This seems a great leap ; the sepal and the petal of a rose have no

similarity. But let us put aside the rose and pass to her flowers. Even in the peony some connection between a sepal and a petal can be traced in the red border of the former and in the notch of the upper part ° atter . ( v S ' S ' ) ’ which is similar to that in the sepa ( g. 7, ught hand). In the Camellia, however, we are thoroughly perplexed as to where the sepals end and the petals begin, so gradual and unnoticeable is the passage from the hard green sepal to the delicate white or red petal. So a petal is nothing but a modified sepal, which in its turn is a modified leaf. It follows that a petal is nothing but a leaf.

Let us now peep into the inside of a flower, and choose for our purpose one of the larger flowers, say a lily. From the centre of the flower several organs project, composed of a thin stalk, on the top of which are inserted crosswise two yellow oblong sacks split longi- tudinally. The slit discloses a dr} 7 dust, orange in colour, the pollen. These organs are called the stamens ; the receptacles containing the pollen are the anthers, and the stalk bearing them the filament. One would think that a stamen and a petal have no connection whatever. But let us look for a suitable illustration before jumping to a conclusion. Probably every one is familiar with the white water-lily, so common in our streams and ponds, with its large almost round leaves and its flowers floating on the surface of the water. Let us pull one of these white flowers to pieces and spread out its several parts, as we did with the bud of the chestnut, beginning with the outermost, i.e. the external white petals, and ending with the part nearest the centre of the flower, the organ, composed of the yellow receptacles filled with pollen and a filament rather flat in form, in which we easily recognise a stamen (fig. 9) . We notice once again the same imperceptible transformation : here is a typical white petal ; on the top of it appear two yellow spots, which increase in size as the base of the petal becomes narrower ; two oblong receptacles become clearly marked, and the base of the petal transforms itself into a narrow filament. Here at last is a real stamen, the anthers of which split longitudinally and shed the pollen. The petal has passed into a stamen. The possibility of such a transformation is proved

by horticulturists who produce reverse transforma- tions, changing stamens into petals. Such staminate flowers changed into petaloid are called double . 1 Take, for example, the common peony. It has five petals and many stamens, but the double peony has many petals and correspondingly few stamens. On closer observation we shall become convinced that the inner petals are the transitional form of stamens : on the edge of the bright red, slightly wrinkled petal are situated

yellow anthers more or less w r ell developed. In the dog-rose, which is the prototype of our rose, we notice only five petals and a great number of stamens ; in the rose some of the stamens have been transformed into petals: this is why their number is greater than five. Double flowers are also of interest from the physiological standpoint, because they can be produced artificially. The outer scale-leaves of the bud can also be artificially transformed into real leaves. We there-

1 In Nature as a rule the different parts of flowers probably appeared in the same way as in the case of the double flowers just described, i.e. the stamens were transformed into petals, and not the petals into stamens. fore reach the conclusion that the transformation of one kind of leaf into another can be demonstrated not only by observation, but also by means of experiment, generally by far the more convincing method. Proceeding with our study we reach the very heart of the flower. After the stamens we meet the last organ of

a flower — I say the last because it forms its cen- tral part and thus terminates its growth and consequently the growth of the part of the stem which ends in the flower itself. This organ is called the carpel or pistil on account of its form, which, with its swelled base (ovary), elongated neck (style) , and rounded top (stigma) is very like a pestle. There may be one or many carpels in a flower. The lowest part of a carpel, the ovary, is hollow inside, so that the whole organ in this illustration (fig. io, flower of cherry) is like a small bottle. This cavity contains one, several, or even many bodies, round and white, called ovules. We meet this organ again with distrust. This time there seems to be not a trace of likeness to a leaf, but another successful choice of illustration will prove that this organ also is derived from one or many little leaves. Some abnormal flowers will give us the necessary clue. For instance in the double flowers of the cherry the carpel often transforms itself from a bottle-shaped organ into tiny leaves, one or two in number (fig. n). 1 In many cases it is even unnecessary

1 A — Pistil partly transformed into a leaf. B — The same pistil in a transverse section. C — Pistil transformed into two leaves. to refer to abnormal plants to see the leaf-like character of the carpel and the resultant fruit. It is enough to glance at the fruit of a legu- minous plant, such as a bean, or still better the fruit of the | peony, to be convinced that | it is nothing but a leaf, the edges of which have curved f. over and grown together, thus jlMv forming an organ with a longi- /] tudinal join (suture) with a I W hollow space inside. In other Sa k cases the ripe fruit in bursting r§ shows quite clearly that it con- a b c

The carpel, then, has been derived from one or more little leaves modified in form. But not in all ab- normal flowers are the carpels transformed into real leaves as we see it in the cherry. In other cases the carpel transforms itself into organs more closely related to it, such as stamens and petals. The transforma- tion of a pistil into a stamen can sometimes be studied in the flower of a willow. Occasionally bright red petals can be found in the centre of double peonies with white, shiny ovules on their edges. These are surely carpels which have become transformed into petals, but which have kept their ovules. It follows that a pistil can transform itself into all the preceding organs, i.e. into stamens, petals, and real green leaves. Does not this prove that all these organs are of one and the same origin ?

In our analysis of the plant we have reached its topmost organ — the carpel ; we cannot proceed any further — we can only go deeper into the interior of the carpel, the cavity of the ovary. We shall find there ovules, as has already been said. What are these ovules ? In the flowers where carpels have changed into green leaves we notice small green leaflets or whole leaf-buds on their edges at places where we should expect ovules. But what becomes of the ovule — not the abnormal one, which grows into a green leaf, but the ordinary '

of new plants. Here evidently our description of the external features of a plant ends. I have unrolled before j you the whole picture of the outward manifestations of the life of the plant. We started with the seed and we have returned to it, and have thus completed the full '' enumeration of organs, which is indispensable for my subsequent exposition, by linking them together by the one leading idea of transformation or the metamorphosis ! point of view the life of a plant is like a phantasmagoria, >■

An organ has only time to assume before you a definite shape, when it already loses its configuration, becomes 1 j then gradually becomes again more distinct, appearing this time in another form, as another organ, and so on : the one replaces the other, the one passes imperceptibly into the other, until the whole cycle of development is closed and the primary and original organ reappears. So far we have had only the leaf organs in view, but beside them the body of the plant reveals two other organs, the beginnings of which are to be found already in the seed : these are the stem and the root, the structures which support the leaves. These two organs, apparently so different and growing in different environments, are in some rare cases, however, capable of transforming themselves into each other : the stem sinks into the soil and assumes the character of the root, or the root grows up into the air, covers itself with leaves, and assumes the character of the stem. Hence the stem and the root, forming the axis of which they are the two modified forms adapted to different conditions of existence, and the appendage of the axis — the leaf — with its manifold variations (scales, petals, stamens, and so forth) are the fundamental external organs produced by a normally developed plant during its life-time.