The Life of the Plant

CORRESPONDING MEMBER OF THE ACADEMY OF SCIENCE, ST. PETERSBURG A glance at the preface to the first Russian edition, will, I hope, convince the English reader that I was fully aware of the exceptional difficulties of the task I had undertaken. Seven editions in the course of thirty-five years have in a certain degree contributed to dispel my fears, but on being asked to give my assent to this English translation I experienced afresh the same feeling of diffidence at the prospect of addressing a new audi- ence. Just at that moment I came across that admirable article by Professor Armstrong on The Future of Science in our Schools . 1 I was glad to see that not only in its general tendency, blit even in the choice of matter and in the order of exposition, my book seemed to answer the present requirements of English schools as formu- lated by so eminent an authority as Professor Armstrong. The inspection of the table of contents of this book will suffice to show that even in details it agrees with the short programme proposed by Professor Armstrong (/. c . p. 438, 439) ; both begin with the analysis of flour and culminate in an exposition of Darwin’s theory.

4 The main thing we ought to teach our youth is to see something.’ This maxim of John Ruskin, chosen by Professor Armstrong as a heading to his article, has ever been present to the author of this book. A pair of healthy eyes and occasionally a good lens is all that is required 1 Presidential Address to the Association of Public School Science Masters, delivered January 13th, 1910. Science Progress , January 1910, p. 417. to see the external forms of our common plants. But how different is the case when we are expected to show even the commonest phenomena of plant life, for the most part invisible, and in so many respects quite dif- ferent from the familiar manifestations of animal life! — think only of respiration without inspiring and expiring, or of feeding on air. At every step we require more or less complicated, or, what is highly desirable but not so easily attainable, the simplest possible apparatus . 1 Moreover, all the results obtained must be considered from the general point of view of those two sister (or rather mother) sciences — physics and chemistry. In this respect I have consistently complied with Professor Armstrong’s precept to which I readily subscribe: ‘ Whatever we teach in our schools, chemistry must not be neglected ; it is the science of life, life being but a succession of chemical changes : it is therefore the basis of physiology.’

I fully expect that not a few of my botanical colleagues may consider some passages of chapter vii. out of date ; but I must frankly confess I consider a return in a certain sense to the sound notions of Andrew Knight or A. P. De Candolle, of Dutrochet or Hofmeister may prove to be a desirable corrective to the alarming spread of the ‘ Reizphvsiologie ’ with its morbid outgrowth of ' Neovitalism ’ and ‘ Phvto-psychology,’ and their natural corollary, anti-Darwinism. Nowadays in our pursuit after the quasi-nervous stimuli we have nearly lost out of sight the object stimulated and the mode of action of the external agents. No less an authority than Sir Joseph Thomson has recently warned us that

1 I may perhaps be allowed to add that I believe I was the first to introduce lecture experiments into my annual courses on plant physiology, which began in 1870. At least, at a much later date, Professor Julius Sachs, the head o£ the German school of physiologists, as 1 was told in 1877 by one of his assistants, never introduced any ‘ Vorlesungsversuche ' into his lectures. even in the higher realms of science * something more grossly mechanical, a model, is felt by many to be more suggestive and manageable, and for them a more powerful instrument of research.’ ... I realty think that some such models as those formerly proposed by De Candolle for the heliotropic effect or by Hofmeister for the elucidation of geotropism, adapted of course to the growing exigencies of the time, might bring back the study of the mechanism of growth to a more promis- ing field of research.

That the ideas I venture to advocate are not so utterly out of date may be inferred from the fact that similar ideas have- been recently advanced by a repre- sentative of a much younger generation of botanists, by the regretted Professor Barnes . 1 For my part, I am as firmly convinced as I was forty years ago that the 4 mechanistic conception 9 and Darwinism have been bequeathed by the 4 wonderful century ’ to the still infant science of plant physiology as the two sure guides for its further evolution, and I may adduce in support of this opinion the eloquent testimony of the late Professor Boltzmann : 4 If I were asked, how will

our century be called by the coming generations — the century of iron, of steam, or of electricity? — I would reply, in all earnest, it will be called the century of the mechani- cal interpretation of nature, the century of Darwin .’ 2 * It is impossible for me to bring to a close this pre- fatory notice without expressing my best thanks to 1 1 In fact there is an inclination after endowing protoplasm with such properties as a irritability,” “ automaticity,” and “ self-regulation,” to be satisfied with these words and there make an end.' — ‘ I propose only to present some suggestions on the matter of these phenomena as a con- tribution towards a mechanistic conception of plant/ . . . The Nature of Physiological Response. The Botanical Gazette , New York, 1910, pp. 322-

2 Das zweiie Haaptgesetz dev mechanischen Warmetheovie , 1S86. Populate Miss Cheremeteff for having undertaken and success- fully completed this translation. As a foreigner I am, of course, not entitled to judge of the literary merits of the translation, but on the other hand, having carefully read through the whole of the proofs of this volume, I am bound to bear witness to the many and considerable difficulties overcome by the translator. My warmest thanks are also due to my colleagues, Pro- fessor Seward of Cambridge and Professor Vinogradoff of Oxford (lately of Moscow), for their friendly help with regard to the publication of the book.

For about a quarter of a century there has been a great gap in the botanical literature of the west of Europe, as also of Russia, since there has been no book that might inform the public in a popular way of the present state of vegetable physiology. I decide to publish these lectures in the hope, were it only in slight measure, of meeting this end. J n submitting this book to the judg- ment of the public, I fully realise the difficulties of the undertaking. Every popular exposition, precisely be- cause of its popular nature, deprives the author of the possibili ty of expressing the whole truth, i.c. of criticising from all sides the facts he brings forward; and, more- over, it obliges him not to say anything but the truth, a requirement that can scarcely be complied with in a science which is far even yet from being firmly estab- lished. Hence it is clear that a popular exposition of such a science as the physiology of plants presents many more difficulties than a similar exposition, for instance, of chemistry or physics.

The second requirement for such a book is that the author should give up for a while his usual point of view, that of a specialist; and should, so to speak, step back a little in order to see what science looks like at a distance. The main condition for success consists in the selection of such a point of view as will be close enough to allow of the observation of main details, and yet not too dose to spoil by detail the impression of the whole. 1 1 is not for me to decide whether I have been fortunate enough to find such a point or not.

The position of an author of a popular book differs also from that of an author of a special treatise, in that he is deprived of any opportunity for self-justification or defence. He surrenders himself defenceless into the hands of his judges. The reader appears as his first and last court of appeal. A specialist may consider his exposition to be conscientious, to have overcome considerable difficulties ; but if his work so much as displeases the reader, it will fail of its aim and be therefore doomed.

I hope that I may find as kindly critics among my readers as I had the privilege of finding in my audiences. They have appreciated the difficulty of my task, and have indulgently criticised its fulfilment . 1 1 These lectures were delivered during the winter of 1876 in Moscow The Plant _as a Source of Energy,’ placed in the appendix, was delivered at St. Petersburg in the spring of 1S75. In presenting this book to the English public my sincere thanks are due to my friend Miss E. I. M. Boyd, AI.A., who kindly undertook the revision of the MS., and has shown the closest interest in the translation and its publication.

I should like also to acknowledge a debt of gratitude to Professor Seward of Cambridge, and Professor Vinogradoff of Oxford for their kind help in regard to the publication of the book. My best thanks are due to Air. D. Thoday, of Trinity College, Cambridge, Lecturer in Plant Physiology in the University of Alanchester, for his valuable assistance in the matter of scientific revision and the correction of proofs. The general public's meagre knowledge of botany. Two old- fashioned types of botanists. The contemporary trend of science. Morphology and physiology; form and life. Two reasons for the comparative backwardness of botany ; the logical and the practical reason. Art and science. Agriculture and the physiology of the plant. Science and the general public in mutual relationship.

Survey of the external organs of a flowering plant. Meta- morphosis. Spore-bearing plants — of earlier date and simpler in structure than seed-plants. A spore — a cell. The cell — the foundation and beginning of every organism. These facts in relation to the problem of the origin of organisms. Treat- ment of subject ....... i Law of the conservation of matter. Origin of plant-substance —in the external environment. Elements and compounds entering into the composition of plants. Three fundamental groups of chemical compounds : albuminoids, carbohydrates, fats. Chemical and microscopic investigation of the plant.

Absorption, of nutrient substances by the plant. General conception of the diffusion of matter. Diffusion of gases and liquids. Colloids and crystalloids. Transformation of substances in the cell explains their absorption. Fundamental mechanism of the nutrition of the cell . . . . 35 Structure of the seed and external phenomena of germination. Three conditions of germination : water, air, heat. Mechanical function of water. Chemical function of water. Ferments. Diastase. Pepsin. Insectivorous plants. Independence of the parts of the embryo. Artificial nutrition of the embryo. Mechanism for the translocation of the nutrient substances in the plant.

absorption of oxygen— respiration. Loss in weight and rise of temperature as a result of respiration. Importance of the surrounding temperature. Temperatures : maxima, minima , and optima. Effect of the age of the seed on its germination. Longevity of seeds. General characteristics of the period of germination. Division of labour between different organs of the plant, already apparent in the lowest plants . . 59 Function of the root. Composition of the soil. Method for defining the necessary nutrient substances. Artificial cultures. Cultures without organic matter. Water cultures. Importance of nitrogen, potassium, iron, silicon. The necessary nutrient substances absorbed by the root. Nutrient substances in the soil for immediate use and in reserve. Absorbent properties of the soil. Importance of saltpetre in the soil. Assimilation of nitrogen by leguminous plants. Form in which nutrient substances are found in the soil.

Structure of the root. Its striking elongation and the purpose of this character. The root in relation to liquid and solid substances. General mechanism for the absorption of nutrient substances by the root . . . . .88 Function of the leaf. The nutrient substance assimilated bv the leaf. The leaf in relation to carbonic acid. Structure of the leaf. Evolution of oxygen. Decomposition of carbonic acid in water. Obviousness of the experiment. Decomposition of carbonic acid ' in an artificial mixture of gases and in the atmospheric air. Formation of a carbohydrate (starch) in the chloroplast.

The decomposition of carbonic acid from the point of view of the transformation of energy. . Nutrition of the plant at the expense of organic matter. Fungi and parasites. Physio- logical functions of the leaf . . . .. Function of the stem, secondary as a medium between the leaf and the root. Forms of stems. Internal structure. Cell, fibre, and vessel. Three types of tissue: nutritive, mechanical, and conducting. Connective tissue and bundles. Structure of stems in monocotyledonous and dicotyledonous plants, Wood and bark.

Ascending current of water. Its course and destination. Participation of the root— its water-raising power. Participa- tion of the leaves — evaporation of water. Function of the stomata. Function of the vessels. Function of bordered pits. Velocity of the sap. Purpose of the cork tissue. Movement of nutrient substances formed by the leaf. Course of this move- ment. Function of the sieve and latex-tubes. Causes of this movement. Formation of stores of nutrient substances . , 149

Nutrition and growth. Direction of growth in the root and stem. Attraction by the earth. Tnrgidity of tissues. Mode of action of gravity. Influence of light. Heliotropism. Methods of measuring growth. Influence of temperature. Thermotropism. Growth and multiplication of cells. Division of the nucleus. The proximate effect of light on the growth of the cell-walls. Effect of pressure on the form of cells. Growth mechanism of ceils. Possibility of hearing plants vegetate. The art of experiment . . . . . . .182

Sexual and asexual reproduction of plants. The flower. Essential parts of the flower — ovule and pollen. Fertilisation. Fertilisa- tion in the lowest plants. Adaptations securing the fertilisation of flowering plants. F unction of the so-called non-essential parts of a flower. Self- fertilisation and cross-fertilisation. Co-operation of wind and insects. Parts of the flower attracting insects. Special forms of flowers adapted to cross- fertilisation by insects. The part- played by art in the production of cultivated varieties. Purpose of selection. Insufficiency of physiological knowledge of the nature of the sexual process . . . . .225

Current ideas as to the difference between plants and animals. Capacity for movement in a plant. Microscopic movements : of protoplasm, zoospores, and antherozoids. Movements of organs in the highest plants under the influence of external conditions (heat, light) . Sensitive organs. Mechanism of these movements. Spontaneously moving organs. Utility of various movements. Similarity between the internal processes of movement in plants and animals. Similarity in the processes of nutrition. Similarity in the process of respiration. Respiration and fer- mentation. Similarity between the phenomena of stimulation

and anaesthesia in plants and animals. Is a plant capable of consciousness ? The difference between plants and animals is not that of quality but of quantity— not in kind, but in degree. The sum-total of experimental physiology does not exhaust the problems of the science . . . . .252 The adaptive character of organic forms can be explained only by the historical process of their development. Palaeontology, morphology, and embryology together testify to the genetic connexion between organisms. This conclusion conflicts with the once prevalent conviction as to the permanency of species.

Are species really invariable ? Logical fallacy underlying this opinion. Why does the historical process lead to perfection ? Darwin's theory. The struggle for existence and natural selection. Explanation of the absence of transitional forms. What we have to be content with in explaining particular cases of adaptation. Analytical and synthetical paths followed by the reader. General conclusion and aim of the course . .289 Twofold significance of food for the animal organism — as a building material and as a source of energy. Conception of work and energy, actual and potential. Law of the conservation of energy. Mechanical theory of heat. Chemical affinity. The animal organism, considered as a mechanism. Combustion and respiration.

Necessity for the existence in nature of a process the inverse of combustion and respiration. Priestley’s discovery. Decom- position of carbonic acid by the plant. This process considered from the point of view of the theory of the conservation of energy. Robert Mayer. Production of organic matter by the plant. Chlorophyll, its optical properties, and the explanation they afford of its function in nature. Economic value of the process taking place in the green organs of plants. Theoretical limit to the productiveness of the earth General inference

It is not, I think, much beside the mark to say that the word ‘botanist’ still calls up in the minds of many even well educated people not conversant with science one of two pictures. Either they expect in the botanist a tedious pedant with an inexhaustible vocabulary of double-barrelled Latin names, sometimes most barbarous, who is able to name at a glance any kind of plant, and also ready on occasion, it may be, to describe (quite incorrectly) their medicinal properties — the type of botanist who bores one to death and is certainly incapable of exciting any interest in his subject : or, on the other hand, ‘ botanist ’ depicts the somewhat less sombre figure of the passionate lover of flowers, who flits like a butterfly from one bloom to another, admiring their bright colouring, inhaling their perfume, singing the praises of the proud rose and the modest violet — in other words, the elegant adept of the amabilis scientia, as botany was called in olden times. These are the two extreme types associated in the minds of so many people with the word ‘ botany,’ and I am afraid I know it by personal experi- ence! A botanist is either a pedantic nomenclator or an amateur horticulturist, an apothecary or an aesthete ; but in no sense is he a man of science. The real man of science seems to stand screened behind these types, if such a person as a scientific botanist exists at all. And, after all, what kind of science is botany ? What are its aims ? What are the ideas which control it, v A

if it is indeed working out any ideas at all ? If the public seems ignorant on these points, the fault lies partly with botanists themselves, and partly with the historical development of science. Let us consider these conditions. Living organic Nature meets us under a twofold guise. We find her in bodily forms, i.e. in plants and animals, and we observe her in phenomena, i.e. in life itself. We call living beings organisms, because they are made up of organs or instruments. Every organ, every instrument has a certain function peculiar to itself, and bears at the same time a certain relation to the general life of the whole organism. It is impossible to study organs apart from their function, or organisms detached from their life — almost as impossible as to study a piece of mechanism and its parts without regard to their function. Who would have the patience to study the description of the parts of a mechanism, say of a clock, without any explanation of their function ? Such a study would be not only tedious but fruitless. Likewise it is obviously impossible to become acquainted with the working of a machine without knowing its con- struction. It follows that the independent study of an organism from the two arbitrary points of view mentioned above, i.e. in relation to its form and its functions, is artificial and even illogical. These artificial points of view r , however, and a corresponding division of the subject, long ago became established in science. Biology, the science of living beings, was split into two branches : (i) the study of forms, called anatomy or, more generally, morphology, and (2) the study of phenomena, of life, called physiology. This division was caused partly by the necessity for applying the principle of the division of labour to the manipula- tion of such large numbers of accumulated facts, partly by differences in the methods of investigation, and also partly by difference of aim in the two branches of this

particular science. The one observes and describes, the other experiments and explains. The impossibility of carrying such a division of the subject to a logical issue proves how artificial it is. In fact it can never be strictly applied. The morphologist is bound to describe the function of an organ and the physiologist its struc- ture. Nevertheless, this division of the science of botany, and particularly the narrow specialisation of scientific activity, threaten to become a serious danger for the future, a confusion of tongues as at Babel : for surely the morphologist will cease to understand the physiologist, and the physiologist will cease to take interest in the work of the morphologist: every specialist will shut himself up in his narrow province, without troubling himself as to what takes place out- side of it. The existence of these two provinces is, nevertheless, an inevitable fact, owing to a necessity against which it is entirely futile to demur.

It is nevertheless clear that these two provinces are capable in very different degree of attracting general attention, the attention of people not conversant with science and only interested in its supreme achievements. A simple description or enumeration of the plants and animals about us cannot excite any general interest, although the number of people who find pleasure in an acquaintance with the native flora and fauna does prove a certain degree of scientific development in the public. The fragmentary description of remarkable plants and animals arouses but little interest, being too hackneyed, and suitable only for children’s books, or for occasional illustrated publications for grown-up people. General attention may perhaps be attracted by some marvel, such as a carnivorous plant devouring living people, an absurdity which appeared some time ago in many foreign papers as well as in our own dailies, and even slipped into more specialised publications.

tion of phenomena common to all the organisms of both kingdoms, the study of the fundamental laws of life. This can and must attract the attention of all thinking men who wish to understand what is going on around them. The same holds true in the inorganic world. Mineralogy, which is a simple description of matter that forms the crust of the earth, certainly cannot excite the same interest as chemistry, which explains phenomena taking place as the result of the reaction of substances, or as geology, which recites the history of our planet.

There is no doubt therefore that physiology rather than morphology, function rather than structure, and life rather than form, may be expected to attract general attention. Let us now see which of the two tendencies has been the more fully worked out in botany — is, it the one which deals with life or the other which con- fines itself to lifeless forms ? The history of science shows that botanists have spent nearly all their energies upon the latter kind of work. Men of science have devoted themselves entirely to that extreme of the subject, forgetting the life of which the body is but the vehicle. At no very distant period the great majority of botanists belonged to the first of the types described above, and even to-day not a few may be found ready to repeat the words of a French zoologist who, in the course of an exciting debate in the Paris Academy, prided himself upon the fact that during the whole of his scientific career he had not expressed a single idea, but had only defined and described, described and defined. If we turn from the exponents of such old-fashioned ideas to our con- temporary scholars, we shall find many who may criticise their predecessors and recognise the superiority of the physiological tendency of the present day, but who nevertheless work along the same exclusively morpho- logical lines. According to these modern scientists, a