 Section 27 of The Science History of the Universe, Volume 6. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Melanie Young. The Science History of the Universe, Volume 6. Edited by Francis Roehler. Botany. Chapter 7. Physiology of Plants. Every living organism has the power of producing offspring which inherit the characteristics of the parent's stalk, says Pfeffer in his Physiology of Plants. The fact that the acorn always produces an oak, a fungus spore the same specific fungus, is sufficient proof that it is the inherent properties of the living substance of the embryonic organism which primarily determine the shape, character and individual peculiarities of the adult organism. In the young plant, the full development of such characters takes place only through interaction with the external world and not unless certain necessary conditions are fulfilled. Thus, if the plant is deprived of nourishment, it finally dies of hunger. While vital activity and growth are only possible in the presence of water and within certain limits of temperature. It is evident that the absence of any one of the necessary conditions must invalidate the remaining ones so that if the amount of water is insufficient, or if the temperature sinks too low, the vital activity of the organism is depressed or completely arrested. And similarly at a high temperature death ultimately supervenes. Hence physiology is primarily required to determine the powers and possibilities of individual organs and cells and their various interactions. The manifestations of life when traced back to their ultimate origin are always found to originate in the protoplasm, an undifferentiated mass of which constitutes the substance of the simplest living elementary organism. Hence one of the tasks of physiology is to throw light on the manner in which the inherent nature of the protoplasm is responsible for the chemical and physical changes to which it gives rise. It is as impossible to picture a regular continuance of life otherwise than by the cooperation of different organs and biological elements as it is to imagine a watch which could still keep time after the removal of certain of the wheels. The chemical nature of the living organism with its indissolubly connected chemical and mechanical properties is of much greater importance than that of a machine. For in the changes which take place in the self-regulating protoplasmic mechanism, chemical nature and affinities are in all cases of fundamental importance. Hence progress in physiology necessarily goes hand in hand with progress in chemistry. From a physiological standpoint, it is hardly possible, for example, to overestimate the importance of a complete knowledge of the chemical constitution of the protides which take so prominent a part in building up the living protoplast, especially in view of the possibility that each particular species may be characterized by a specific variety of living protein. There is no reason for regarding life as the product of an extraordinary and mystical natural force. It is to be treated simply as a special and peculiar manifestation of energy. Moreover, since we can only guess at the evolutionary history of the organism, it is only possible for us to deal with the physiological and other properties which it now possesses. And however clearly we may be able to explain the peculiarities of a given plant as being due to characters and tendencies inherited from its parents, we shall still be unable to determine with certainty the evolutionary origin of that particular species. The production and hereditary transmission of variations are connected in many ways with the general physiological problems with which we are immediately concerned. When any variation takes place, an alternation in the structure or nature of the protoplast must have previously occurred. Provided the variation is not merely a temporarily induced one, but is one capable of hereditary transmission to the offspring. This is true for the lowest as well as the highest plants and whether the variation is perpetuated by sexual or asexual reproduction. The conclusion that a change of this kind necessarily indicates an alteration in the arrangement or character of the protoplasmic constellation is indeed a logical necessity. Even though it is impossible to determine exactly how the given variation arises or is induced, the reproduction of hybrid forms is evidently due to the combination of two different kinds of living substance. There can be no doubt that if it were possible to interchange the nuclei of two separate and distinct protoplasts, assuming that the strange nuclei and protoplasts could live and grow together, two new organisms would be produced differing from one another and from the original protoplast. These special characteristics of the new organisms would be preserved so long as the union and cooperation between the parts of the new protoplasts were maintained. This would also be the case if, for example, a bacterium existed in intimate and permanent symbiotic union with the protoplast as a chloroplast it does and were transmitted from generation to generation in the ovules. It is, as a matter of fact, not inconceivable that the existence of certain species as such depends upon protoplastic or symbiotic unions of similar character to the above. Nor is the possibility excluded that the tiny symbiote might be too small to be visible or might be unable to continue an independent existence outside of the protoplast. Comparatively recently, Lycans were regarded as distinct organisms, although we now know that they are the products of a synthetic union of two distinct plants and that by the artificial synthesis of various algae and fungi in new forms or forms similar to those already known may be produced with relative ease. Nevertheless, as is well-known, variation capable of hereditary transmission may arise without the help of foreign protoplasm and certain bacteria afford especially instructive examples of these. Thus, in many bacteria, the power of forming either spores or certain metabolic products may be inhibited by a particular mode of treatment and in some cases, this inhibition is permanent so that even under normal cultural conditions, a reversal never takes place. The variety thus produced will hence remain constant in a neutral environment, although there always remains the possibility that by the action of other agencies, a return to the original condition may be induced. Accidental reversions are, as is well-known, by no means uncommon in the higher plants. Sultatory variations often do appear in organisms and may arise under precisely similar external conditions in particular individuals only or may even affect these in different manner or degree. It has previously been stated that physiology must necessarily seek an explanation of all vital processes in the developmental and formative powers of the protoplast. Our knowledge on this point is still in its infancy and we must be content if we can gain here and there a glimpse into the internal protoplasmic mechanism. Even though our knowledge with regard to the structure of protoplasm or to be enormously increased, we should still see not the causes and forces which are acting, but only the results which they produce. The most perfect mental picture of the plant or of the protoplast must necessarily fail to reveal the hidden and invisible causes which make it assume its specific form. Above all, it must be remembered that the simplest protoplast is an organism of very complex structure and that its various activities result from the interactions of its component parts and organs. The particular result which any given cause produces is due to the special nature of the given protoplast. Every plant must therefore necessarily have certain special protoplasmic characteristics which are peculiar to it alone. At the same time, protoplast of similar origin may temporarily or permanently acquire special properties by a progressive differentiation of labor and by adaptation to special aims and purposes. Nevertheless, the plant protoplast so long as it remains living retains all the general features which characterize a typical vegetable cell. In order to attain certain ends, the organism forms parts which are not living or capable of life. One such organ is the cell wall which the protoplast constructs as a protective mantle in which it may live and work. Indeed, the protoplast living inside its cell wall may be compared to a snail in its shell. In certain cases, the protoplasmic contents may escape from the cellulose investment as a naked swarm spore which later may build for itself a new domicile. In the protoplast, just as in a snail, the internal structure and functional importance of the component parts require to be studied. Within the protoplast are spaces having considerable functional value which are surrounded by living substance but whose contents are not living. Such are the vacuoles which subserve a variety of functions. They may serve for the storage of reserve food material while the dissolved substances which they contain give rise to the osmotic properties of the cell and preserve these properties during growth. As the vacuoles increase in size, the cell becomes much larger but the amount of protoplasm which it contains undergoes no increase or but little so that finally it is reduced to a thin primordial utricle or bag closely ad-press to the cell wall and containing a single large central vacuole. Vacuoles are laboratories in which food may often be digested or building material prepared for use while at the same time they are utilized in translocation. The body of the protoplast the protoplasm as we may call it is built up of organs and elemental structures. The nucleus is an organ of very general importance and indeed a separation into nucleoplasm carioplasm and cytoplasm probably occurs in all protoplasts. On the other hand chromatophores including chlorophyll corpuscles are organs of special character and are absent from fungi. When such special organs are present they may be given the general name of plastids. Like all living substance the plasmatic organs are of considerable complexity. This is readily perceptible in the resting nucleus and is admirably shown when the latter divides. While the chromatin fibers which are then so markedly visible may also be seen to have a definite structure of their own. Besides the plastids already mentioned the cytoplasm may contain minute bodies often in great numbers which regardless of their morphological and physiological nature may be termed microzones or micro somata. They may be composed in some cases of non-living substance but in other cases may be minute living plastids. In a small cell or one of the organs of such a cell the component units must necessarily be still smaller and yet have positive dimensions. While the smaller and more numerous these units are the more varied and complicated will the possible combinations be. At the same time a relatively greater surface area is correlated with the smaller size and this is a factor of the utmost importance. For bacteria teach us what remarkable powers are conferred by extreme minuteness and what extraordinary processes it renders such organisms capable of performing. The various operations which are continually going on in the body of the plant involve the execution of a considerable amount of work. This is very evident in the enormous development of a large tree from the relatively small seed. Such a process of construction has involved the preparation of a vast quantity of highly complex material from very simple chemical substances. The process is incident to life also though they may not lead directly to the formation of such substances cannot be conducted without involving a considerable amount of work whether the plant is a minute body consisting of a single protoplast or an organism of a much higher degree of complexity. If we turn now to consider the sources of the plant's energy continues J. Reynolds Green in his introduction to vegetable physiology. It is evident that they must be in the first instance of external origin. The radiant energy of the sun indeed is the only possible source which can supply it to normal green plants. The rays which emanate from the sun are generally alluded to as falling into three categories those of the visible spectrum, those of the infra-red and those of the ultra-violet. The second of these are frequently spoken of as heat rays and the last as chemical. The greatest absorption of energy appears to take place in consequence of the peculiarities of chlorophyll. This substance whether in the plant or when in solution in various media absorbs a large number of rays in the red and in the blue and violet regions of the spectrum together with a few others in the yellow and the green. The solar spectrum after the light has passed through a solution of chlorophyll is seen to be robbed of rays in these regions and hence to present the appearance of a band of the different colors crossed by several dark bands. The greater part of the energy so obtained in the cells which contain the chloroplasts is at once expended partly in constructing carbohydrate food materials and partly in evaporating the water of transpiration the latter process being much the more expensive. Speaking of these carbohydrate food materials H.M. Richards says it is evident that the starch which is the first substance that we readily recognize is not the first substance which is formed. Modern research points more and more to the conclusion that it is the simplest of carbohydrates that is produced a substance known as formaldehyde but what is especially interesting is that it seems not impossible that this primal reaction may not after all be a function of the living protoplasm but a chemical reaction that can be carried on outside the cell through the agency of chlorophyll. It is in the further elaboration of this first substance formed that the living protoplasm is apparently necessary. At any rate we know that the energy demanded for the process must be afforded by the particular rays of sunlight which the chlorophyll absorbs. There is plenty of evidence continues green of the power of plants to avail themselves of the heat rays. Not only can the air rob the plant of heat by radiation but when its own temperature is high it can communicate heat to it in turn. Indeed its absorption by the leaves would be a source of considerable danger to the plant for it not for the cooling effect of transpiration which dissipates 98% of it during bright sunshine. No doubt this dissipation is one of the chief benefits secured by transpiration. It is evident however that in the general economy of the plant something further must be at work in connection with the supply of energy. The absorption of these external forms must take place at the exterior of the plant while many of the processes of expenditure are carried out in parts which are more or less deep-seated. We are obliged to turn our attention therefore in this connection as in that of the construction and utilization of food due processes of accumulation distribution and economy. What is the immediate fate of the energy absorbed? It enters the plant in what is known as the kinetic form. A very considerable part of the kinetic energy of the sun's rays we have already seen is devoted at once to the evaporation of the water of transpiration. But some of it is employed by the chloroplast to construct some form of carbohydrate. The energy so applied can be again set free by the decomposition of this formed material. If the latter were burned its combustion would be attended by the evolution of a certain definite amount of heat. This heat would represent the energy that had been applied to the construction of the material so burned. Any accumulation of material in the body of the plant represents therefore not only a gain of weight or substance but a storage of energy. This has disappeared from observation during the constructed processes but can be liberated again during their decomposition and applied to other purposes. Energy which has thus been accumulated and stored is known as potential energy to distinguish it from the actual or kinetic energy originally absorbed. The formation of material in the plant therefore involves a storage of energy in the potential form. And wherever such material is found there is in it an amount of energy which can be liberated with a view to utilization at any point to which the material has been transferred. The protoplasm itself contains a store of such potential energy. It can only be constructed at the expense of food supplied to it. The formation of the protoplasm which follows the supply of food to the cell involves work and the energy so used is partly changed from the kinetic to the potential condition. When the protoplasm undergoes what we have called it's self decomposition which is continually taking place a certain amount of this potential energy is liberated and can be observed and measured in various ways. When destructive metabolism is active there is usually a rise of temperature as in the processes of the germination of seeds. A certain amount of the liberated potential energy in this case manifest itself in the form of heat. A vegetable cell which obtains no direct radiant energy from without can consequently obtain the energy it needs from within itself by setting up decomposition either of its own substance or of certain materials which have been accumulated within it. The transformation of potential into kinetic energy is associated with decomposition just as the converse process is bound up with construction. Destructive metabolism in the cell is then the means by which its energy is made available. The processes of this catabolism go on in the interior of each cell. Each liberates at least as much energy as it requires for the maintenance of its life and the discharge of its particular functions. The processes associated with the utilization of the stored energy are then chemical decompositions in which various constituents of the cell are involved. These are of two kinds in the first of which the protoplasm itself takes part in which comprise the processes in which its own breaking down takes place. In the second it affects the splitting up of other bodies without a necessary disruption of its own molecules. Respiration is to be looked upon as a process very largely connected with the utilization of the store of energy which each cell possesses and perhaps primarily to be concerned in the transformation of that energy from the potential to the kinetic form. The oxygen appears to be necessary mainly for the purpose of exciting those decompositions of the protoplasm which are so dependent upon its instability. End of Section 27 Recording by Melanie Young Section 28 of the science History of the Universe Volume 6 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer please visit LibriVox.org Recording by Madison Rutherford The Science History of the Universe Volume 6 Edited by Francis Roltweeler Botany Chapter 8 Growth and Variation In studying the growth of plants says Reynolds Green the relation which it bears to the processes of metabolism must be born in mind. The constructed processes are much greater than those which lead to the disappearance of material from the plant body. The result of this is that there is a conspicuous increase in the substance of the plant as well as an accumulation of potential energy which can be made use of by the plant through various decompositions which its protoplasm can set up. The great permanent accumulation of material is what we associate with the processes of growth. Mere increase in weight in an organ does not, on the other hand, necessarily imply any growth. Growth, he continues, is in the strict sense always associated with the formation of new living substance and is generally accompanied or immediately followed by additions to the framework of the growing cells or organs. It is nearly all cases attended by a permanent change of form. This is perhaps not so evident in the case of axial organs as it is in that of leaves and their modifications though even in them it can be detected to a certain extent. It is much more conspicuous in the case of leaves for the latter as they expand from the bud have usually a different shape from that of the adult ones and the assumption of the mature form is a gradual process taking place as the age of the leaf increases. Growth may, in the light of the considerations just advance, be dend as permanent increase of bulk attended by permanent change of form. Growth in the lowliest plants may be co-extensive with the plant body. In all plants of any considerable size however, it is localized in particular regions and in them it is associated with the formation of new protoblasts. In the sporophytes of all the higher plants there exist certain regions in which the cells are merismatic, that is which have the power of cell multiplication by means of division. In such regions when a cell has reached a certain size which varies with the individual, it divides into two, each of which increases to the original dimensions and then divides again. As these growing regions consist of cells, the growth of the entire organ or plant will depend on the behavior of the cells or protoblasts of which its merismatic tissues are composed. The growth of such a cell will be found to depend mainly upon five conditions. One, there must be a supply of nutritive or plastic materials at the expense of which the increase of its protoblasts can take place in which supply the needed potential energy. Two, there must be a supply of water to such an extent as to set a certain hydrostatic pressure in the cell. Three, the supply of water must be associated with the formation of osmotic substances in the cell or it cannot be made to enter it. In the absence of the tergesins which will be the result of the last two conditions no growth is possible for reasons that will presently appear. Four, the cell must have a certain temperature for the activity of a protoblast is only possible within particular limits which differ in the cases of different plants. Five, there must be a supply of oxygen to the growing cell. Four, as we have seen, the protoblast is dependent upon this gas for the performance of its vital functions and particularly for the liberation of the energy which is demanded in the constructed processes. This is evident also from the consideration that the growth of the cells is attended by the growth and service of the cell wall and as the latter is a secretion from the protoplasm a product that is of its catabolic activity such a decomposition cannot readily take place unless oxygen is admitted to it. Growth so far as it implies only the formation of living substance is thus a constructive process. It is, however, intimately associated with destructive metabolism or catabolism the latter being involved in the construction of the increased bulk of the framework of the cell or cells and being essential to supply the energy needed for the constructed processes. The process of the growth of a cell is limited in its extent though the limits vary widely in different cases and some cells grow only to be a few times their original dimensions and others they may attain a very considerable size. In any case, however, we can notice that the rate of growth varies regularly throughout the process. It begins slowly increases to a maximum and then becomes gradually slower till it stops. This time during which these regular changes in the rate can be observed is generally spoken of as a grand period of growth. Closely connected with the metabolic activities of the plant and the release of energy for life processes is the phenomenon of digestion. In the simplest conception digestion means merely the rendering soluble and assumable of insoluble food substances but the active agents of digestion the enzymes may and in all likelihood do have a far more intimate connection with the life of the cell than the mere preparation for absorption of food exterior to the actual living substance. The process of digestion in plants continues green is chiefly intracellular and takes place in all cells in which reserve materials occur. It is only occasionally that it is found taking place on the exterior of the plant that is not in the interior of a cell. In a few cases it is carried on in connection with absorption nitrogenous or protein food as has been already shown. Digestion though most generally associated in plants with the utilization of reserve materials may thus occasionally be met within connection with the absorption of food from without when it is a process precisely similar to the digestive processes of the higher animals though is somewhat simpler in the details of its mechanism. The intracellular digestion of plants agrees very closely with that of many of the humbler animals and corresponds also with such processes in the higher forms as a utilization of the glycogen of the liver and the fat of various regions. Absorption of food from without after preliminary digestion is much more frequently observed than when we study the nutritive processes of the fungi. Not only protein but also carbohydrate and fatty substances are thus digested outside the body of the plant and the products of the digestion are subsequently absorbed. The protoplasm of the cell among its many properties no doubt has the power of setting up these decompositions and probably in many of the very lowly plants in which the whole organism consists of only a few protoplasts or perhaps a single one the work is altogether affected by its instrumentality. The protoplast in fact carries out all the various processes of life by the interactions of its own living substance with the materials absorbed by it aided in the constructed processes by the chlorophyll apparatus if it possesses one. In such a protoplast we may observe at times the storage of such a reserved material as starch and its digestion at the appropriate period. Even in more complex plants it is certain that the living substance of every protoplast is in a constant state of change initiating many decompositions in which its own substance takes part as well as others into the course of which it does not itself enter. Among these decompositions we must include the various intracellular digestive processes. Though all protoplasm has this power it is not usual in plants any more than in animals to find it exclusively relying on it. The work of digestion at any rate is generally carried out by peculiar substances which it forms or secretes for the purpose. We have in plants a large number of these secretions which are known as enzymes or soluble ferments. The action of these enzymes is not at all completely understood. They appear not to enter into the composition of the substances which are formed by their activity and they seem to be capable of carrying out an almost indefinite amount of work without being used up in the process. They are inactive at very low temperatures but affect the decompositions they set up freely at the ordinary temperature of the plant. As the temperature at which they are working is raised their activity increases up to a certain point which varies slightly for each enzyme and is called its optimum point. This usually ranges between 30 and 45 degrees Celsius. If the temperature is raised above the optimum point the enzyme becomes less and less active as it rises and at about 60 to 70 degrees Celsius it is destroyed. The exact point however varies a good deal in the cases of different enzymes. Enzymes work most advantageously in darkness or in a very subdued light. If they are exposed to the bright sunshine they are gradually decomposed the violet and ultraviolet rays being apparently most powerful in affecting their destruction. They are often injuriously affected by neutral salts, alkalizer acids though in this respect there exists considerable diversity throughout the group. The enzymes are manufactured by the protoplasm of the various cells in which they occur being produced from its own substance in a manner somewhat similar to that of the formation of the cell wall. Usually their presence is accompanied by a marked granularity of the protoplasm due to the formation in it of an antecedent substance known as a zymogen which is readily converted into the enzyme. This granularity does not however always occur though we have reason to suppose that the secretion of the enzyme always takes place by successive stages. The zymogen has not however been definitely detected in all cases. While as has been stated the digestion of substances within the cell is the most common occurrence there are right a few cases even among the highly developed plants where digestive ferments are excreted and act upon materials exterior to the cell itself. The absorption of food materials stored in the seed is often an instance of this but more strikingly is it seen in the so-called carnivorous plants such as a sundew etc. that were so carefully investigated by Darwin. In the latter case these plants can actually utilize the available nitrogenous material presented in the form of animal substance. In short meat. This process of extracellular digestion is however more especially the attribute of the strictly parasitic or saprophytic plants notably the lower fungi and the bacteria. Of necessity they must digest from the substratum in which they grow the necessary food material unless it happens to be presented to them in soluble and diffusable form a circumstance of rare occurrence. The bacteria are the most important as well as familiar of such plants and as producers of enormously vigorous fermentation for their size there are no organisms which approach them. Their fermented power has long been made use of in many industries and at the present time is the special study of preventive medicine in endeavoring to fully understand and guard against the deleterious effects of disease breeding bacteria on the human organism. Associated with bacteria in a purely physiological sense and no other are the highly degenerate fungi known as yeasts the power of which in producing extracellular alcoholic fermentation has been known in a purely empirical way since prehistoric times. Tomanes, toxins indeed some of the poisons associated with so-called toastools and snake venoms are all enzymatic or fermentative in their nature and a very small quantity of them is capable of producing relatively enormous changes in the substances on which they act and come under the general physical class of catalytic agents. The present aim of bacteriological research as applied to disease organisms is to discover the best mode of combating the toxins and that has been found in the antitoxins which have the power of uniting the toxins and rendering them harmless. Although it must be said that the manner in which they do this is not fully understood. The study of all classes of enzymatic substances and the living organism plants as well as animals is at present the field which promises more than any other to elucidate the mysteries of life processes and with the aid of modern physical chemistry the next few decades may mark a striking advance in man's knowledge of what living protoplasm really consists. The life of every plant is of limited duration to quote from the textbook of botany by Strasburger not shank and karsten death ensues sooner or later and the decayed remains form a part of the surface soil. All existing vegetable life owes its existence to the capacity inherent in all organisms of reproducing their kind. Reproduction is accordingly a vital power which must be exercised by every existing plant species. It is also evident from the very nature of reproduction that in the production of new organisms a process of rejuvenation continually is being carried on. The descendants commence their development at a stage long since passed over by the parents. The physiological significance of sexual reproduction is not once apparent in many plants the vegetated mode of reproduction is sufficient to secure the necessary multiplication of the species so that plants are able to continue without sexual reproduction. Since monogenetic reproduction is sufficient for the preservation of the species sexual reproduction must answer some purpose not attained by the vegetated mode of multiplication for otherwise it would be altogether superfluous at the same plant in addition to the vegetative should also possess the sexual form of reproduction which is so much more complicated and less certain. What makes di-genetic reproduction especially different from monogenetic is the union of the substances of the parents and the consequent transmission and blending of the paternal and maternal properties. It is in this qualitative influence that the chief difference between sexual and vegetative reproduction is shown and this may be regarded as a special advantage of sexuality. By vegetative reproduction the quantitative multiplication of the individual is secured while by sexual reproduction a qualitative influence is exerted. The vegetatively produce progeny consists of unmixed descendants the sexually produce offspring on the other hand are the results of a blending of the parents. In vegetative multiplication the complex of properties unfolded in the descendants does not as a rule differ from that possessed by the parent form. The sexually produced offspring on the other hand endowed with the properties of the father can never be identical with the mother plant but possess the properties of both parents. When these are divergent they frequently play very different parts in the descendants some dominant characters appearing conspicuously while others recessive characters become less marked or remain completely latent and this way the descendants do not exhibit a uniform mean between the parents but some may resemble the father others the mother. These relations determine the character of the sexually produced descendants variations appearing in single individuals will unless they are of an absolutely dominating character become modified and ultimately lost by crossing with ordinary individuals. In such a case sexual reproduction tends to maintain the constancy of the species. In other cases as when one parent possesses new and dominant characters or on both parents tend to vary in the same direction the deviation from the ancestral form may be maintained or increased by sexual reproduction. The greatest tendency to variation commonly exhibited by hybrids illustrates how the equilibrium of the complex properties of a sexually produced individual is affected by divergent parental tendencies. But even as a result of ordinary fertilization not only small and readily disappearing variations or fluctuating variations but sometimes more striking ones occur in which the offspring differs so strongly from the parents and characters which can be inherited that it appears to be a new species or subspecies. In such sudden variations the occurrence of which Von Collicker and with them Korschinski term heterogenesis while devries more recently calls it mutation these authors seek the starting points of the origin of new species. This would occur when the particular species passes from unknown causes into a period of mutation such as devries demonstrated experimentally in Ganathara Lamarckiana the fluctuating variations which largely determine the valuable characters of economic plants. Example given the high percentage of sugar and the sugar beat are in contrast to the mutations not fixed on inheritance. Careful and continued selection of the varying progeny is thus necessary to maintain the required standard of the race. Hugo de Vries himself says and writing on this manner of variability. Before Darwin little was known concerning the phenomena of variability. The fact that hardly two leaves on a tree were exactly the same could not escape observation. Small deviations of the same land were met with everywhere among individuals as well as among the organs of the same plant. Darwin was the first to take a broad survey of the whole range of variations in the animal and vegetable kingdoms. His theory of natural selection is based on the fact of variability. His main argument is that the most striking and most highly adapted modifications may be acquired by successive variations. The direction of the adaptations will be determined by the needs and the struggle for life and natural selection will simply exclude all such changes as occur on opposite or deviating lines. In this way it is not variability itself which is called upon to explain beautiful adaptations but it is quite sufficient to suppose that natural selection has operated during long periods in the same way. Eventually all acquired characters being transmitted together would appear to us as if they had been simultaneously developed. Correlations must play a large part in such special evolutions. Darwin repeatedly laid great stress on this view although a definite proof of its correctness could not be given in his time. Such proof requires the direct observation of a mutation. The new evening primaroses which have sprung up in my garden from the old form of Genathara Lamarkeana and which have evidently been derived from it in each case by a single mutation do not differ from their parent species in one character only but in almost all their organs and qualities. Some authors have tried to show that the theory of mutation is opposed to Darwin's views but this is erroneous. On the contrary it is in fullest harmony with the great principle laid down by Darwin. In order to be acted upon by that complex of environmental forces which Darwin has called natural selection the changes must obviously first be there. The manner in which they are produced is of secondary importance and has hardly any bearing on the theory of descent with modification. A critical survey of all the facts of variability of plants and nature as well as under cultivation has led me to the conviction that Darwin was right in stating that those rare beneficial variations from time to time happen to arise. The so-called mutations are the real source of progress and the whole realm of the organic world. The origin of new species which is in part the effect of mutability is however due mainly to natural selection. Mutability provides the new characters and new elementary species. Natural selection on the other hand decides what is to live and what to die. Mutability seems to be free and not restricted to previously determined lines. Selection however may take place along the same lines in the course of long geological epochs thus directing the development of large branches of the animal and vegetable kingdoms. In natural selection it is evident that nutrition and environment are the main factors. But it is probable that while nutrition may be one of the main causes of mutability environment may play the chief part in the decision ascribed to natural selection. Dr. Daniel T. MacDougall in a lecture published in 1905 tells us that scattered through the literature of botany and horticulture of the last century are scores of records of the sudden appearance of sports and forms of the aspect of species which fully support all of the conclusions drawn from the observations on the evening primroses. An examination of the facts easily brought together allows us to see that certain general principles in the organization of the plant and in its behavior in these breaks or saltations and heredity may be made out. The first and most important of these is one which was advanced by DeVries speculatively before he began his experiments and heredity. Namely that the plant is essentially a complex group of indivisible unit characters. These unit characters may not always be expressed or recognizable in external anatomical characters since they may be in a latent condition or totally inactive. Popular belief in the influence of environment and the inheritance of acquired characters finds its common expression and that plants have been changed by cultivation. Domesticated races are spoken of as garden forms by botanists and horticulturists with the implication that they are specialized types resulting from the effects of tillage. Now so far as actual cultivation is concerned this assumption is without foundation since at the present time no evidence exists to show that the farm garden or nursery has ever produced alterations which were strictly and continuously inheritable or were present except under environic conditions similar to those by which the alterations were produced although vague statements and erroneous generalizations to the contrary are current. It is true of course that structural and physiological changes may be induced in a strain of plants in any generation which may persist in a share to the second or even in some degree to a third but no longer. Some very important operations of the market gardener and the farmer are dependent upon this fact. The matter of general scientific agriculture opens an immense field says H. M. Richards. The scientific care of our forest for trees may be regarded as a crop and their culture agriculture is a question to which we in this country are awakening none too soon. Forestry as practice in Europe demanding as it does expert botanical knowledge perhaps not by the foresters themselves but by those who direct their labors has saved what were the fast diminishing wooded areas. The scientific rotation of crops the use of fertilizers and the study of the physical and chemical condition of the soil in connection with the living plants continues Professor Richards involves certain questions which may mean the success or failure of much farming. These questions can only be settled by careful investigations which take into consideration the nature of the plants themselves as well as the physical conditions of their environment. Some say that knowledge along this line has been satisfactorily handed down from father to son that the farmer knows his business better than does the scientist but is a patent fact that this is not so. For instance many a farm which has been damaged for a long period of years by the over liming of the soil might have been spared had the farmer of 50 years ago had the knowledge which we now have of the relation of lime to the other mineral substances needed by the plant of one to apply it and one to withhold it. It is a difference between merely empirical knowledge and that which is based on scientific principles. When the contest comes between virgin soil and long-tailed land the latter no matter how rich it may once have been must needs be cultivated more intensively if it is to hold its own. Intensive cultivation requires the aid of special information and it is here that scientific agriculture comes into play. Few people realize that without artificial fertilizers the direct outcome of highly theoretical work on the raw foodstuffs of plants much of the farming of today would be almost impossible and the properties of fertilizers is but one of many questions. We are coming now in this country to a stage in its development when scientific agriculture must be seriously considered. Fortunately it is being so considered and the federal and state establishments devoted to the investigation of these agricultural questions may confidently be expected I think to help in the solving of the practical economic questions that must arise in the competition of our own agriculture with that of other lands. The way it must be done is by the introduction of improved methods based on carefully conducted scientific research that often find their stimulus in the highly theoretical investigations of the peer scientist. Thus must the so-called impractical devotee of science come in contact the practical man of affairs and furnish him knowledge that can be used for the benefit of all. End of Section 28 Botany Growth and Variation Recording by Madison Rutherford. End of the science history of the universe Volume 6 Zoology and Botany Edited by Francis Rotewheeler.