NEW ACHIEVEMENTS IN CONTROLLING THE NATURE OF PLANTS
T. D. Lysenko
Lecture delivered on July 6, 1940, at a conference of heads of Marxism‑Leninism departments at higher educational institutions—Ed.
I INTEND to deal with only one problem of the big subject of controlling the nature of plants, namely, the role of environmental conditions in the development of plants. To the present day 'this problem has evoked great and heated discussion in the scientific world. While some scientists recognize the role of environmental conditions in moulding the nature of organisms, others consider that environmental conditions, the conditions of life, cause no alteration in the nature of organisms, or that, if they do, the alteration is in any case not a qualitative one. The former are Darwinist‑Michurinists, the latter Morganist‑Mendelists.
Let us analyze the fundamental postulates of each of these trends in biological science.
As you know, living matter at one time originated from nonliving matter. Although we do not know the conditions under which the first living beings appeared, or the time of their appearance, for Marxists it remains an incontrovertible fact that the living arose from the nonliving. Further you also know that all organisms (whether they be animal or plant) build themselves up only out of nonliving matter. In other words, every living organism builds itself up out of food (in the broad sense of the word). Plant organisms absorb minerals from the soil and gaseous substances from the surrounding air. These inorganic substances are converted into organic matter by the plant organism, which from the products thus converted builds all the organs and all the parts of its body. Simultaneously with the process of assimilation a process of dissimilation takes place in the organism. The two processes are inseparable, integral. All this is common knowledge, and is undisputed in science.
Further. The various plant organisms differ from one another. Anyone of you can observe the great diversity of plant organisms in nature or in practical agriculture. One comes across scores of different plants in any small patch of grass or woodland. Each one of these plants possesses its own specific properties. In a small kitchen garden bed for example, both pepper and tomato may be growing. One of these plants bears sweet fruits, the other bitter. Moreover, there are different varieties of pepper; some varieties produce sweet, others bitter fruit. Nor are these differences limited to sweetness or bitterness. Wild and cultivated plants or their fruits differ in form, colour, size, etc. Two plants may grow literally side by side; they may have the same environment‑the same soil, the same air, the same light, and yet they develop differently, form different bodies. Both plants build themselves up out of the substances that occur in one and the same environment, but the results are different. The organisms produced are not the same and can easily be distinguished.
Why is this so?
To this question the answer of plant breeders is unanimous: it is so because different organisms, as, for instance, the pepper and the tomato, have different natures. Nor is there any disagreement among scientists on this score. Each organism builds itself up out of food that surrounds it; but each organism does so in its own way, for each of them has its own nature in accordance with which it lives. Each organism absorbs substances from its environment that correspond with its nature, and these substances and the conditions elected from the environment by the particular organism are then modified and converted by it in its own peculiar way.
The difference in the behaviour of organisms in one and the same environment is explained by the difference in their natures, or, as it is expressed in modern biological science, by the difference in their genotypes.
It would be only natural for you to ask: but what about the breed, the genotype, itself; is it built up or not, does it alter or not? If the breed, the genotype, builds itself up, develops, changes, then the question arises: how, from what, and under the influence of what forces does this take place?
It is on these questions that the opinion of scientists is divided. A dispute has long been raging around these questions among biologists. This dispute has become particularly acute in our country of late.
In our country, where agriculture is being built up on strictly scientific principles, great practical interest attaches to the question of how to control the nature of organisms, of how we can and should improve the nature (genotype) of organisms according to a definite, assigned plan. Obviously, before replying to this question the biologists must decide as to whether the nature (i. e., the genotype) of organisms is mutable or not. Perhaps the genotype is not subject to change at all?
I am confident that the answer to this last question is clear to everyone here. To you the variability of the nature of organisms is axiomatic. But the variability of the nature of organisms, this indisputable law of life, is far from being an axiom to everyone. Both in 1938 and in 1939 a number of periodicals in the Soviet Union published articles by scientists contradicting what is self‑evident to all of you, and to me in particular.
There are still quite a number of scientists in our country who consider the nature of organisms immutable. These scientists argue that the breed of an organism, the genotype, is a special substance consisting of particles, a "hereditary substance," intrinsically different from the ordinary substance, from the body of the organism. The "hereditary substance" (called by Academician Koltsov "genoneme") is allegedly not subject to change, does not undergo transformation in the life process of the organism. Hence it appears that the general law of life—the process of assimilation and dissimilation—is not applicable to the "hereditary substance." Thus, for instance, not so long ago one such scientist, the above‑mentioned Academician Koltsov, wrote:
"Chemically, the genoneme with its genes remains unchanged in the course of the entire ovogenesis and is not subject to metabolism—oxidation and reduction processes."
It is not often that one comes across such undisguised metaphysical assertions in journals published in the Soviet Union. After all, not every editor by far will let such things go through. However, we quoted Academician Koltsov from a journal edited by Academician Koltsov himself. This explains why lines which nohow hang together with the generally recognized conceptions of the laws of life came to be printed.
But there are not a few scientists in our country who, although they are essentially in agreement with Academician Koltsov, make their contention that the nature of the "hereditary substance" is immutable in a disguised, veiled manner. They do not assert (but neither do they deny!) that the "genoneme" is not subject either to oxidation or reduction processes. Such a contention would, indeed, be too glaring a contradiction of all the conclusions of science. These geneticists verbally admit the mutability of the genotype, but at the same time they say: We do not know how this change takes place in the genotype, but we do know that it is not through assimilation and dissimilation.
Such scientists actually differ in nowise from the scientists who altogether refuse to admit variability, since both in their journals, works and textbooks they maintain that the quality of the genotype's variability does not depend on environment, on the organism's conditions of life.
Let us take wheat, for example. The scientists whose views we are now analyzing say the following: irrespective of whether wheat grows in cold or in warmth, the nature of the plant is not altered in any way, and even if a change does take place, the quality of this change does not depend on cold or warmth. In other words, according to this point of view, the very same changes can take place in the nature of an organism in either cold or warmth if the state of the organism is the same.
Such is the contention of the Morganist geneticists. The Darwinist‑Michurinists maintain the opposite: changes in the genotype, i. e., in the nature of a living body, correspond to changes in the body—the soma—occurring under the influence of environmental conditions. It is this proposition that at present constitutes the pivotai point of the controversy about the variability of the genotype and the ways of controlling this variability.
It is necessary to examine the question under discussion from all angles. Perhaps changes in the nature of organisms and the quality of these changes actually do not depend on external conditions?
Perhaps environmental conditions are only a stimulus with regard to changes in the breed of organisms, a spark, so to speak, falling into a powder magazine? The powder explodes for inherent reasons, and the spark merely sets it off, simply raises the temperature where it comes into contact with the powder.
The Morganists who propound such theories frantically attempt to prove that their theories follow directly from Darwinism. They strive to demonstrate that their contention that the quality of genotypic variations is independent of the quality of the environmental changes derives from Darwin's teaching. Hence, they declare, we are one‑hundred‑per‑cent Darwinists. In their opinion, the people who claim that environment is not a matter of indifference as regards the quality of an alteration in the nature of organisms are nothing but Lamarckians.
In this connection, let us remark that it is idle for the Morganists to try to terrify people by accusing them of being Lamarckians. Lamarck was a wise man. But his teachings, of course, cannot be placed on the same level with Darwinism. There are serious errors in Lamarck's theory. But Lamarck was the most progressive biologist of his day. It is wrong to make a bogey of Lamarck. Men of science who know their business have no reason to be afraid of Lamarck. They take what is good from his theory and discard what is false.
But that is not the point. The Morganists do not understand and do not admit Michurin's thesis that variations in the breed of an organism are bound up with the conditions of life of the given organism. They endeavour to label this thesis Lamarckism, although it is an organic part of Darwinism.
The basis of Darwinism is the theory of natural and artificial selection. Recognition of the theory of natural selection is conducive to a correct understanding of the formation of the genera, species and varieties of animals and plants. Artificial selection, on the other hand, makes it possible for man consciously and deliberately to create better races, better varieties. It is only by natural selection that one can explain the amazing harmony, so to speak, in nature, the adjustment of organisms to their environment‑to the season, to the soil; the adjustment of the organs to one another within the organism, etc. Look around you in a forest or fieldno sooner does a caterpillar appear than right beside it you can see a leaf already beginning to unfold. The leaf is board and lodging for the caterpillar. It seems to have developed especially for the latter. One might wonder: how is it that this caterpillar did not emerge two weeks earlier? Simply because if it had been born before the leaf appeared that would have been the end of it.
In nature, of course, only relative adjustment, harmony, cooperation, exist. At the same time a struggle is going on, mutual destruction, some organisms surviving by devouring others, etc.
The principles of Darwinism are known to you. Therefore I shall not dwell on this question in detail. I shall only point out that Kliment Arkadievich Timiryazev, who did so much for the further development of Darwinism, often said and wrote that Darwin's expression "natural selection" must be understood metaphorically, figuratively. Darwinian selection, wrote Timiryazev, involves three phenomena: variability, heredity, and survival.
In order to select anything (in artificial selection), or for anything to be selected in nature, what is necessary above all else is variability of organisms. Variation provides the material for selection. The variations themselves may be beneficial, injurious or immaterial to the organism. However, for selection to lead unfailingly to the perfection of organisms, not only variability of organisms is necessary, but also the preservation, fixation and accumulation of these variations in the offspring. It is this that is called heredity. Variation creates a diversity of forms, but it is heredity that fixes these new properties of the organisms, while the entire environmental complex of the given organism and the interaction of the latter with the external conditions determine the fate of the organism in nature, i.e., decide whether it will survive or perish, whether it will have offspring or not.
We agrobiologists cannot regard selection as a mere sieve, cannot refrain from taking an interest in how and why a given variation occurs, how and in what conditions it is fixed and becomes transmissible. In studying selection, we are obliged at the same time to study the phenomena of variability and heredity. If we fail to study the laws governing these phenomena, we shall be able to understand the development of organic forms from less perfect to more perfect ones only in its most general aspect. But we shall not be able to discover the concrete laws of development of organisms. In that event progressive development in nature will, of course, take place independently of us, just as was the case hitherto. In practical farming, however, things are altogether different. If we are to bear practical ends in mind it is impermissible, intolerable to reduce Darwinism simply to the selection of ready forms. Unless we know concretely how to produce such variations of organisms as we require and how to make them hereditary, we agrobiologists cannot become proficient in our work.
We cannot, and have not the right, to sit and wait for the time when, for instance, in a field sown to wheat a single spike, out of the tens of thousands of other spikes there, will appear, possessed of a new character of importance to farming. We cannot wait passively for a spontaneous variation, and at that a variation we desire Moreover, we should be unable to tell whether this variation would be fixed, whether it would be preserved in the offspring. For lack of knowledge, we would be unable to help matters. Such passivity and such ignorance are incompatible with, contradictory to, the revolutionary spirit of Darwinism.
Practice and science that want to make use of Darwinism as a guide to action stand to gain very little from passive waiting and dependence solely on the selection of ready, random forms that appear independently of man. It is incumbent upon us to learn to alter and direct the nature of organisms in accordance with the requirements of man. At the same time, we must be able to fix the variations already produced, to make them heritable, and to select for further breeding the best of these changed organisms, those most fully answering our desires and requirements.
The branch of science that treats of the control of the variability of heredity has been very little developed to this day; the causes of variation in the nature of organisms have been little studied as yet. Darwin himself did not do much to elaborate this branch of science as applied to practical farming, and therefore contemporary Darwinism is inconceivable without the work of Michurin, Timiryazev and Burbank, and without taking into account the enormous amount of scientific data and facts that have been accumulated as a result of the work being done in this field in the Soviet Union.
I shall endeavour as I go along to tell you in brief how we Darwinist‑Michurinists understand the development of plants, the role of environmental conditions in the development of plants, how we understand the role of environment in the creation of an organism's body and in the creation of this organism's nature.
There is no need to dwell on the role of environment in creating the body of the organism. Everyone knows that the better the conditions provided for a plant, the higher will be its yield. Yield now depends on the collective farmers who know the rules of scientific farming. The Stakhanovite collective farmers, the followers of Yefremov, fully understand that the plant builds itself up out of the food that surrounds it. It all depends on man whether more or less food is given the plant and whether this food is of a better or worse quality. Agrotechnique teaches us how to provide plants with more and better food so as to obtain big yields. I shall not deal 'here with this branch of science.
Let me now pass on to the role of external conditions in creating the nature of the organism, the genotype.
It is common knowledge that every organism possesses its own nature, or, to use the scientific term, its own genotype. In essence, breed, nature, genotype and heredity are all synonymous. Scientists say genotype; the collective farmers say breed, nature. Actually, one and the same thing is meant.
Every organism has its own nature; rice has its own, and wheat has its own. It is characteristic of the nature of rice that it requires relatively definite external conditions, peculiar to itself. Wheat, in its turn, also requires specific environmental conditions. For instance, rice requires the field in which it is grown to be inundated with 5‑7 inches of water. Such conditions, which are favourable and even indispensable for rice, would prove fatal to wheat. Not only does wheat not require the same conditions as rice but it cannot even bear such conditions.
The nature (genotype) of each of these crops was formed historically and is usually extremely conservative. People have been engaged in agriculture for hundreds and thousands of years, and still rice invariably requires a surface covering o water, while wheat, on the contrary, cannot stand it. Two different organisms can live arid develop in the same environment, yet they will build themselves up in different ways because they absorb different substances from the environment and absorb them in different ways, transforming or modifying these substances differently.
It is this that constitutes the heredity, or nature, of an organism, as the property of the organism, of the living being, to draw on the environment for just those substances, those conditions of life, that are suitable, specific for it, and to absorb, assimilate them.
The property of heredity is the capacity of the organism to take from the environment only what agrees with the nature of the given organism and not to take whatever does not agree with it, even when the conditions that the nature of the given organism requires are lacking. This, in my opinion, is what constitutes the property of heredity.
The property of heredity is conservative. The conservatism of heredity expresses itself in the fact that if the conditions which the nature of the organism demands do not exist, the organism will not accept, will not assimilate, different conditions, conditions that do not agree with its heredity, its genotype. It frequently happens that an organism does not find conditions suitable to its heredity, and since it will not assimilate the existing conditions, which are different and unsuitable, it perishes. However, if the organism lacked this conservatism in its choice of conditions of life, the comparative order which we observe all about us in nature would not exist.
Allow me to illustrate this by an example. I assume that everyone here has either heard or read something about vernalization, about the phase of vernalization. Most likely, you have also heard that this phase of development in winter plants necessarily requires cold, in addition to a number of other conditions. If cold is lacking, winter plants will grow, develop roots and leaves, but will not pass through the stage of vernalization. And until winter plants traverse this phase, they can form neither stalks nor spikes even though the conditions of the external environment are suitable for the development of these organs. At a definite stage the nature, the heredity, of winter plants requires cold.
That is why ordinary seeds of wnter wheat which are sown in the spring, when there is no prolonged period of cold, produce plants that will grow and tiller until the autumn, but will not grow stalks or spikes. Today, however, we already know how artificially to force winter plants to bear fruit even if sown in the spring. At the end of the winter, before the seeds of the winter plant are sown, they are moistened with a specified quantity of water. The embryo now begins to grow. The nutriment it needs is contained in the seed itself. The required low temperature (approximately 0º C.) is obtained by regulating the thickness of the layer of moistened seeds. Exact experiments have proved that the slightly‑grown embryo within the seed, even before it breaks through the seed coat, is already capable of passing through the phase of vernalization. After passing through this phase before being sown, winter plants can bear fruit even if they are sown in the spring.
You see before you two tufts of Novokrymka 0204 winter wheat. They were both sown in the spring of this year in Gorki Leninskiye, at the Experiment Base of the Lenin Academy of Agricultural Sciences of the U.S.S.R. One of these wheat plants looks like a tuft of grass. This grass can continue to grow until the autumn, but it will not ear. The other wheat plant is of the same breed, the same variety. It was sown at the same time and, as you see, has already formed spikes and will soon blossom. In somewhat over a month it will yield ripe seeds. The seeds of this wheat were vernalized before being sown. In other words, in the second case seeds were sown whose natural, genotypic demands for the conditions requisite to pass through the process of vernalization had been satisfied. Thanks to this the development of the plant proceeded normally. In the first case, on the other hand, seeds of the same variety were sown, but they had not passed through the phase of vernalization. We did not satisfy the requirement of this breed for vernalization conditions, did not provide it with cold, hence the plant failed to form stems.
In order to obtain a crop from plants, it is necessary to comply with their nature, to satisfy the demands of their heredity with regard to the conditions of development of the given plant as a whole, and in particular of those organs which produce the harvest. The better and more fully we satisfy the requirements made by the nature of the plant, the greater the harvest we shall be able to gather.
The two plants of winter wheat which I have shown you are different in appearance, are different organisms. But their natures, i.e., their heredities, are comparatively the same. The organisms are different, their appearances differ, because the natural requirements of one of these plants were satisfied (it was vernalized), while the natural requirements of the other plant as regards the phase of vernalization were left unsatisfied.
But chilling the suitably prepared (soaked) seeds and thus satisfying their hereditary requirements does not change their hereditary character of being winter plants. That is why we say that the nature of these two different organisms is comparatively the same. If vernalized winter wheat is sown in the spring, we can harvest seeds in the summer. Upon sowing the seeds thus obtained, they will again require cold in order to vernalize, just like all winter plants in general. They will not be satisfied with warmth and will not pass through the phase of vernalization in warmth.
Here we have a very definite manifestation of the conservatism of heredity.
Everyone knows that in addition to winter wheat there is also spring wheat. This wheat is sown in the spring; it does not require the low temperatures that winter wheat requires. In spring wheat the process of vernalization takes place at a higher temperature. This hereditary property of spring wheat is likewise conservative.
What would be the result if the heredity of winter plants, for example, were not conservative?
The seeds of a wild winter plant would ripen in June and then shatter. After a rainfall the seeds would begin to sprout. At this time of the year it is warm, there is no cold. If heredity were not conservative, the plant would not require cold and would easily begin to pass through the process of vernalization in the warmth. After this the stalks, the straw would form. But we know that if cereal grasses evince even the faintest sign of straw formation, the plants are no longer capable of withstanding severe frosts, i.e., of living through the winter. Cereal grasses that have passed through the phase of vernalization and begun to form stalks (straw) are unable to develop resistance (hardiness) to frost.
For this reason if wild winter cereal grasses did not possess the conservative hereditary property of winter habit they would be unable to exist.
What would happen to winter plants in agriculture, in practical farming, if their heredity were not conservative? We should quite simply fail to obtain a harvest.
For hundreds and thousands of years winter plants have been sown on millions of hectares in August and September, when it is still warm. It is only due to the fact that plants have a strongly conservative heredity that winter plants sown in the early autumn, when it is still warm, develop roots and leaves but do not pass through the stage of vernalization. The winter plants do not have suitable conditions for vernalization since it is not cold. That is why these plants are able to live through the winter. In the late autumn and winter, cold sets in and the plants become vernalized,, and in the spring they begin to ear.
When we harvest the seeds of winter plants we may be quite sure that the plants grown from these seeds will also be winter plants, and the offspring of seeds from spring plants will be spring plants. The same is true of all the other inheritable characters and properties of plants. Thus, for example, the offspring of awned wheat will be awned, of red wheat‑red. From these simple examples we may pass to more complex ones, and all of them alike will testify to the conservatism of heredity. The favourable aspect of the conservatism of heredity is that this property makes it possible to have definite varieties in agriculture, while in nature it ensures the preservation of the ability developed by organisms to adapt themselves to their external conditions.
But the conservatism of heredity also has its unfavourable aspects. The stable and conservative property of heredity obliges man to humour plants in every way and to suit conditions to the plant with the help of agrotechnique. This is not always possible or convenient. Hence, the question naturally arises: Cannot the conservatism of heredity be broken? Is it impossible, for example, to force winter wheat to require for its vernalization the warmth that prevails in our fields in the spring, instead of cold?
In order to answer this question we must have a clear conception of how the various heredities are formed and under the influence of what forces they are modified.
The property of heredity inheres in living matter alone. All living matter builds itself up out of food, out of its environmental conditions, by means of assimilation and dissimilation. More than that, the very first living matter arose from nonliving matter. But if life originated from nonliving matter and every plant organism builds up its body from such matter, from food, it naturally follows that all the inherent properties of the living body—including the property of requiring specific conditions of development, i.e., the property of heredity—develop, build themselves up and change simultaneously with and inseparably from the development of the very body of the organism.
We already have at our disposal a vast amount of factual material, both experimental and practical, which shows that not only the body of the organism but its heredity as well builds itself up in the process of development, i.e., in the process of absorption, of assimilating the environmental conditions of the organism.
Diverse hereditary characters are conservative in diverse degrees, but all of them are to a certain extent conservative. Such a hereditary property as the winter habit of grain is one of the most conservative properties. For thousands of years people have been obtaining winter crops from the winter plants they sowed. From the seeds sown in the autumn grass would sprout, in the spring stems would form, and then spikes and grain. During the autumn, winter, spring and summer thousands of changes would occur in the plant, every day would bring some new transformation, and at the end of the ripening apparently the same seed, with the very same hereditary properties, would be obtained as was originally sown.
But if one examines matters a little more closely, it is not difficult to see that the nature of the organism does not remain unchanged from generation to generation, but also changes. These alterations are of different degrees, from those that are scarcely noticeable to quite considerable ones. We have in view here changes that occur when we humour the plant, when we meet the requirements of its nature.
But what would happen if the plant were not provided with the conditions it requires and given other conditions? What would be the result of this? You could reply: "The plant will not accept conditions that do not suit it, will not assimilate them, and as a result will perish." That is true. However, it is not always so.
If one approaches the plant from the standpoint of the Michurin theory, if one treats the plant organism properly, it is possible not only to increase the yield by humouring the nature of the organism but also to remould its very nature, its very heredity, in accordance with the conditions prevailing in the particular bed, field or garden. In other words, the heredity may be changed deliberately in the direction we desire. This can be done by means of skilful training of the plant.
What, then, does this skilful training of plant organisms consist in?
It consists not only in humouring the plant's nature but also in opposing it with a view to inducing new demands in the given plant.
Winter habit is one of the stable hereditary properties of cereals. In farming it is absolutely necessary to cater to the requirements of winter plants with the help of agrotechnique and to furnish them with cold, otherwise there will be no harvest. But what would be the result if we "mistreated" winter wheat Novokrymka 0204 and did not provide it with the conditions essential for vernalization? The result would be no crop. A study of the biology of winter wheat has shown that the different varieties require different periods of chilling for vernalization. Novokrymka 0204 requires a temperature of approximately 0° C. for a period of 35 days in order to go through the entire process of vernalization. If the temperature is 3°-5° C. the process of vernalization will require 40 days. If the temperature is 15°-20° C., the process of vernalization will not take place altogether, or, if it does, will take a considerably longer period of time.
But what will be the result if we chill soaked seeds of this same Novokrymka 0204 for only 25-30 days? Vernalization will proceed normally. After 30 days we cut the cold treatment off. Thus, the seeds will still be 5 days short of the normal period for completing the process of vernalization. From numerous experiments we know that if the period this variety normally requires for vernalization is artificially shortened by even one or two days, the other processes, which follow vernalization, cannot take place. In every phase of the development of the plant organism, including the phase of vernalization, a qualitative change takes place in its demands on environmental conditions. But for this change to take place certain definite external conditions quantitative in character must be available. After the organism has been provided with these conditions and has assimilated them, it suffers a qualitative change, development enters a new phase and the demands of the organism on its environment also change. For example, the demand of winter plants for the cold which they need in order to pass through the process of vernalization is replaced by a demand for warmth. For the phases following vernalization, for the subsequent processes, warmth is now indispensable.
Thus, the soaked Novokrymka 0204 seeds which we chilled for 30 days (we vernalize them that long) are then sown in the field in the spring. It is not very warm in the spring, but neither is it cold. And now, instead of completing the process of vernalization in 5 days, which this sort of winter wheat would do at a temperature of about 0° C., the plant begins to experience distress, figuratively speaking. It "languishes" in this way for 15-20 days, but in the end it completes its vernalization. But once vernalization has actually taken place, despite the abnormality, despite the "distress," further development proceeds at a very rapid pace. The field conditions for this are good: the days are long, there is plenty of light, it is warm and there is sufficient nutriment.
In the summer the seeds of the plants ripen. The question arises: will these seeds be normal, common seeds possessing the normal heredity of the winter variety? It turns out that they will not. In these seeds the old, long-established, conservative heredity of the winter habit has been broken down. In this generation the heredity has not been reproduced as it was in the numerous preceding generations. Cold was not given the plant at a particular, critical moment, towards the end of vernalization.
In our experiment the vernalization was completed in warmth and not in cold. What does this mean with regard to the plant? It is impossible to conceive that one and the same process can take place in a living organism both in cold and in warmth in absolutely the same way. If we take seeds of any variety of winter wheat, divide them into two lots and let the vernalization of one lot be completed in cold, and of the other lot in warmth, then, of course, the processes of vernalization in these two lots of seeds will differ qualitatively. The heredity as regards the phase of vernalization will also be different in the organisms grown from these seeds.
Suppose we sow the seeds of the plants that completed vernalization in warmth. The new organisms, as experiments have shown, no longer stand in particular need of vernalization chilling. They no longer have that urgent need of cold which exists in ordinary winter plants. The old, conservative hereditary property of winter habit has been destroyed by us in 10-15 days, i.e., during the time when the plants of the preceding generation completed the process of vernalization in conditions of spring temperature.
I must state that this is not only easily said but easily done. All that is needed to destroy any conservative hereditary trait prejudicial to the definite end we pursue is a knowledge of the conditions with which the organism should be provided, and when. It is necessary to know when to stop humouring the old, strong heredity, when to remove the conditions which the old heredity requires and to substitute for them conditions for which we wish to create a demand in the organism. I must stress that in this interesting task everything depends on the skill and knowledge of the experimenter.
We tried giving the winter plant warmth at the beginning of the vernalization process instead of at the end. In this experiment, after very prolonged treatment, the heredity changed, but we obtained deformed organisms.
In order to change the nature of the vernalization phase, it is necessary to modify the conditions under which vernalization takes place at the end of the process.
How did we arrive at this conclusion?
Here it would be in place to mention the absolute necessity of coordination between the experimental work of scientists and practical life. Whatever the experiment we undertake, we must always keep an eye on what is happening around us in life. We must examine life closely and try to understand the facts we observe in it and to link them up with the experiment we are working on.
In practical farming, people have been sowing winter wheat for thousands of years in the early autumn, in August, when it is warm (cold sets in much later), and the winter habit of this variety of grain has never changed because of this. Why then provide warmth at the beginning of vernalization? The process of vernalization simply will not take place in this case; the organism will wait for the onset of cold. In order to convert winter wheat hereditarily into spring wheat, warmth must be supplied only at a strictly definite time, namely, before the end of the process of vernalization.
Several researchers attempted giving the plant warmth after earing, when not a breath, so to speak, of the process of vernalization was left; vernalization had long been completed in the given plant. In such experiments these researchers wanted to change a property which the organism had possessed in the past, but which it had already outlived, a property which could reappear only in the succeeding generation. Thus, these people tried to change something in the organism which it no longer possessed at the time of the experiment. They explain this mode of experimentation by asserting that an organism possesses a specific hereditary substance—genes—which in its normal state is not subject to the processes of either oxidation or reduction. As they conceive it, the genes of winter habit are always present in the form of particles in the cells of the winter varieties of plants. Therefore, according to their view, the time of treatment and the state of the organism at that time are of no importance. And despite their obviously incompetent experiments these scientists say that it is impossible to change winter varieties into spring varieties by bringing external conditions to bear upon them.
When we provided warmth for winter plants at the beginning of vernalization, no good results by way of transforming the nature of the plant were obtained. But when we began to provide warmth at the end of the process of vernalization, the results were considerably better—the old heredity was often broken down immediately. On the basis of these experiments we arrived at the following conclusion: the conditions in accordance with which we wish to create a new heredity must be furnished at the end of the process whose nature we are changing.
Today there is not a single hereditary winter variety of wheat that cannot be converted into hereditary spring wheat in two or three generations. From wheats preferring cold at the vernalization stage it is possible, by a proper growth of wheat varieties, to obtain spring forms which do not require cold.
It may be objected: very well, granted that you already know how to break down the conservative hereditary winter habit and to create in its place a hereditary spring habit. This does not yet prove that heredity, as a property of living bodies, is created from and depends on the same nutrition, the same conditions, from which the organism's body is created by means of assimilation.
And indeed, how can we prove, how can we obtain experimental evidence that heredity really depends on nutrition, that it is built up in the process of the formation of the organism's body itself, in full conformity with this process?
Let us turn to experimental examples. In agriculture there are various sorts of tomatoes having diverse heredities. There is, for instance, the Mexican (wild) tomato. The fruits of this variety are small, round, and, when ripe, red. Then there is the cultivated tomato known as the Albino. The ripe fruits of this sort are not small but of normal size, and not red but yellow.
It is known that if a cutting of a tomato plant is grafted on to another tomato plant, the graft, after union of stock and scion, begins to develop. In experiments carried on by A. A. Avakian and M. G. Yastreb (Odessa Institute of Selection and Genetics) a cutting of a young yellow‑fruited Albino tomato plant was grafted on a Mexican red‑fruited tomato plant.
What substances are produced by the roots and leaves of the given red-fruited stock? It is quite clear that they elaborate those substances that are characteristic of the given variety, that are indispensable for the formation of red fruits. Hence the grafted cutting of the yellow‑fruited Albino plant is forced to use nutrients of the red‑fruited variety instead of its habitual food. As a result of such nutrition the yellow‑fruited variety graft frequently bears fruit that are not yellow but red, or reddish, or yellow with red streaks. From this it is perfectly evident that here the nutrition has exerted a direct influence on the quality (in the given case, the colour) of the fruit.
To this, the Morganist‑Mendelists say: true, the quality of the fruit has changed. But that is of no particular 'significance. All agree that the body of an organism changes under the influence of external conditions, including nutrition. But the heredity, they continue, undergoes no change, i.e., remains that of the Albino variety.
On the other hand, we who adhere to the Michurin theory hold that if we were to take the seeds from a red' fruit that had grown on the grafted yellow cutting and were to sow them, the new plants would bear not only yellow fruit but red ones as well. The Morganists were and still are wholly unwilling to admit this, as was evidenced by their speeches at the special conference on questions of genetics called by the editors of the journal Pod znamenem Marxisma in October 1939.
When I took the floor to speak at that conference, I had in my hand only the fruit of the grafted plant. On demonstrating this fruit I said approximately the following: if experimenters succeeded in raising red fruit on a yellow‑fruited cutting, how much easier must it be to obtain red plants from red fruit. After all, in practice people as a rule obtain red fruit from the seeds of red tomatoes and yellow fruit from the seeds of yellow tomatoes.
The Morganists, however, retorted: you will not get them—the body of the fruit has changed but its heredity has not.
This controversy took place in October 1939. In the winter of that same year, the seeds of the red fruit were sown in a greenhouse in Odessa, at the Institute of Selection and Genetics. The requisite time elapsed, the plants grew up, and some of them produced red fruit, others yellow. There were also plants bearing fruits of intermediate colouring ranging from red to yellow.
The same results were achieved by Avakian in Gorki Leninskiye, at the Experiment Base of the Lenin Academy of Agricultural Sciences of the U.S.S.R.
Of particular importance to us is the fact that in addition to the plants bearing red fruit we also obtained plants bearing yellow fruit.
What conclusion can be drawn from the given experiment?
It is possible to draw the direct conclusion that under the influence of nutrition the heredity of the developed graft not only changed in general, but changed in the direction of the heredity of the stock, and this modified heredity was transmitted to the seed offspring. It follows that heredity may be shaped by the agency of nutrition, by the interchange of substances (in this case, between the scion and the stock). By changing the nature of the metabolic process we can achieve the directed alteration of the nature of the organism.
The Morganists seek to prove that heredity is located (in the literal sense of the word) in the chromosomes, in the form of particles. They even draw diagrams showing the position of these particles and the linear arrangement of the genes (the heredity corpuscles). The assumption that these particles are transmitted from one organism to another is precisely what the Morganist chromosome theory of heredity is based on.
But we know that chromosomes are not transmitted to the scion from the root of the stock. The protoplasm was also not transmitted; yet the heredity of the indicated graft underwent a directed change, was "transmitted" from the stock to the scion and vice versa.
In the light of experiments with vegetative hybrids, nothing remains of the Morganist chromosome theory of heredity. Chromosomes, of course, still remain in the cells, and of course they possess the property of heredity just as do other reproductive elements of the body. But the chromosome theory of heredity, i. e., the theory maintaining that the chromosomes differ intrinsically from the rest of the body with regard to heredity, must be thrown overboard in its entirety.
But perhaps what I have related here is an isolated case that involves only the colour property of the fruit?
No, it is far from being the only case of vegetative hybridization. There have been fairly numerous cases where hybrids have been obtained, in other words, where the hereditary properties of two organisms united in a third, new organism; moreover these hereditary properties combined without any fusion of the nuclei of the cells and without fusion of protoplasm.
No few examples of changes in heredity by mean's of grafting could be cited.
These experiments were performed by various people, all of whom, however, hold the same views, basing themselves in biology on the teachings of Michurin. The possibility of vegetative hybridization has been unerringly proved in theory, and as for practice, numerous vegetative hybrids are already being raised in our country.
There is a variety of tomato called Humbert. The fruits of this variety are oblong in shape. They are widely used for canning. The Humbert was grafted on to an early variety having round fruit. The seeds were taken from the graft (the Humbert scion) and sown. The offspring obtained were diverse: there were fruits resembling the Humbert, round fruits, and fruits which were round on top and Humbertian, oblong, below.
This diversity in the shape of the fruits obtained as a result of grafting is extremely gratifying to us, but most depressing to the Mendelist‑Morganists.
Why is that? you will ask. It is because these facts disclose to us a number of interesting regularities.
For one thing, these facts show that the heredity of the stock and the heredity of the scion build one another through the medium of nutrition, through the metabolic processes; what is obtained is, so to speak, a union, a fusion of two breeds.
For another thing, and this is most noteworthy, we see that the old breed can be preserved; in other words, the result is analogous to the result obtained in sexual hybridization.
In sexual hybridization the fusion of two sex cells results in a new organism. This new organism usually possesses a dual heredity‑both paternal and maternal. This dual heredity separates, as it were, in the individual cells, for instance, in the sex cells. The result is what is known in genetics as "segregation." The Morganists explain this separation of the dual characters, this "segregation," as a dissociation of the homologous chromosomes, in which, they assert, the hereditary particles (the genes) are located. One chromosome contains the hereditary properties of one parental form, another chromosome those of the other.
But experiments with vegetative hybrids, I repeat, patently proved that chromosomes are not transmitted from the scion to the stock (or vice versa), whereas hereditary properties may be and are transmitted, and that these hereditary properties of two varieties may combine in one, and may then vegetatively, or through the medium of seeds, again separate, so to speak.
All these facts oblige us to regard the sexual process in an entirely different way from the way in which it has been regarded in biology hitherto. I have not the time to deal with this question in detail. I should merely like to point out that Darwin himself had already foreseen a change in the scientific views of sexual reproduction. Recognizing that vegetative hybridization is possible, he wrote the following:
|1Charles Darwin, The Variation of Animals and Plants Under Domestication, London 1885, Vol. 1, p. 417.|
"... if, as I am now convinced, this is possible, it is a most important fact, which will sooner or later change the views held by physiologists with respect to sexual reproduction."1
The example of vegetative hybrids constitutes splendid proof of the fact that heredity is not only changed under the influence of conditions of life, but is also built up, is created under the influence of these conditions, under the influence of nutrition, of metabolism. In other words, heredity, as a property of living matter, is created under the influence of the very same things as go to create the body of the organism. Vegetative hybrids are excellent confirmation of this proposition.
To us a correct understanding of heredity and its alteration is of the utmost interest. This question is of extreme importance not only in the realm of theory but equally so in actual practice. It is my custom to tackle any question of theory only from the standpoint of practice, to solve problems practically. Nor has this become a habit with me because I do not care for theory. Quite the contrary: divorce from practice leads not only to fruitless but also to erroneous work in the sphere of theory. This may be confirmed by dozens of examples taken from works dealing with theoretical problems in the field of genetics‑‑the science of heredity and variability.
The Michurin theory of heredity and of the means of controlling it furnishes the scientific worker with simple and at the same time very effective methods of remoulding the nature of plants.
In 1935 I did not know of a single instance of spring wheat having been produced from winter wheat. It was not known how to change the hereditary winter habit into a spring habit.
At present, however, anyone who tackles this work can fairly easily convert hereditary winter forms into hereditary spring forms. At the same time we have also learned how to transform spring forms into winter forms. Thus, for example, G. T. Solovey, formerly with the Odessa Young Naturalists' Station, and F. A. Kotov and N. K. Shimansky, both research workers of the Odessa Institute of Selection and Genetics, set themselves the task of procuring winter varieties from spring varieties. And they succeeded in doing so.
In order to convert hereditary winter plants into spring plants it is necessary to bring a higher temperature to bear on the organisms at a definite moment in their lives, in other words, it is necessary to apply warmth to the vernalizing winter seed at a definite moment. Solovey and Kotov did the contrary, i.e., they treated spring varieties with cold. By their nature, spring varieties do not require chilling for vernalization, but nonetheless they were sown in the field in the late autumn and subjected to cold for a prolonged period of time. In this way they forced the spring varieties to change their heredity in the course of two generations and become winter varieties. Now we sow the seeds of these altered plants in the spring, and they no longer behave like spring varieties but like winter varieties; they do not develop stalks, nor do they ear, and they require cold for vernalization.
Such sowings are demonstrated at the All‑Union Agricultural Exhibition. Erythrospermum 1160 wheat is growing on one of the plots there. One half of the plot is sown to the spring variety, the other half to the winter variety that has been obtained from the latter. Both varieties were sown at the same time, in May. At the end of June the spring form has already eared, while the winter form is still in the rosette stage, tillering and showing no signs of coming into ear, since it requires chilling, and there are no prolonged periods of cold.
The endeavours to convert winter varieties into spring varieties, and spring varieties into winter varieties are of interest not only from the theoretical standpoint—for studying the basis of heredity and its alteration. These endeavours open up a new stage in the breeding and seed growing of our cereals.
Not only were the results of the experiments in transforming winter plants into spring ones and spring plants into winter ones such as were expected, but in addition a number of other very interesting and important results were obtained.
Some of the wheat seeds that Shimansky converted from Erythrospermum 1160 spring wheat into winter wheat in the autumn of 1939 were subjected to variety tests at the Institute of Selection and Genetics.
In the spring of 1940 it was evident that this wheat had wintered like a good typical winter wheat. Moreover, when the conversion experiments were made—transforming the spring variety into a winter one—we did not suppose that this winter wheat would be able to withstand the winter cold better than all the varieties of winter wheat coming from the steppes of the Ukraine. But this was just the case.
The winter of 1939‑40 was not a favourable one for winter wheat in the fields of the Odessa Institute. Winter wheat like the Ukrainka (standard) wheat, for instance, was quite badly damaged by frosts.
In these variety tests, the winter wheat developed from Erythrospermum 1160 spring wheat was sown side by side with Ukrainka. A survey of the plots in the spring, after the wintering, revealed that the new winter wheat, developed from spring wheat that was totally nonresistant to frost, was in no way inferior, and even superior, to the hardiness evinced by the standard, Ukrainka winter wheat.
The very same was the case with the winter barley obtained by Solovey from Pallidum 032 spring barley. In variety tests at the Institute of Selection and Genetics all the standard varieties of winter barley almost completely perished in the winter of 1939‑40. The winter barley which Solovey had obtained from spring barley also suffered greatly. But, nevertheless, it withstood the winter incomparably better than all the other, standard winter varieties of barley—its winter hardiness was greater.
Today it has become clearer to me, how to produce a winter variety of wheat such as will be able to resist the severest frosts that occur in regions of the harshest climate, as, for instance, the open Siberian steppes.
This is an absolutely real possibility.
In the two instances I mentioned, the agriculturists had not set out with the purpose of developing frost resistance in plants. We did not try to make these varieties frost‑resistant, they became so of themselves. Now we have a pretty good idea of why this took place.
So long as the heredity of the organism remains conservative from generation to generation, it is very difficult to do anything with the organism; it does not lend itself to rapid improvement. The new winter varieties obtained from spring varieties, however, no longer have the old heredity. It has been destroyed. And the new heredity is just forming in the organism, is no more than a propensity, so to speak. Hence, such heredity is not yet conservative, is unstable. It may be termed destabilized heredity, to use the expression of Michurin and Vilmorin. And organisms with a destabilized heredity are excellent material for the plant breeder. Given skill, remarkable things can be done with this material.
An organism possessing an unstable, destabilized heredity requires conditions that are suitable to it no less than an organism whose heredity is fixed and conservative. But in contradistinction to the latter, which would perish in the absence of such conditions, the organism with an unstable heredity does not wait if these conditions are not forthcoming, but begins to assimilate many others from its environment.
The distinguished biologist and remarkable plant breeder Vilmorin wrote in his time that it was of the utmost importance to induce variations in plants. It is of importance to change plants even if it is in the direction opposite to the one desired, so long as a change is effected. After this has been achieved it is easy to, force the plant with such a destabilized heredity to do what we want it to do. The very same idea has been expressed by the outstanding American biologist Burbank, only in different words. And this idea has been elaborated more profoundly on a scientific theoretical basis by the Soviet scientist Ivan Vladimirovich Michurin. Michurin not only pointed out the definite scientific paths along which to proceed in the question of altering and destabilizing the heredity of plants, in general, but he likewise showed how to induce directed changes. The followers of Michurin have really mastered the technique of making systematic directed changes in the nature of organisms. Today we understand this question much more fully and profoundly than we did yesterday.
Today we not only know how to destabilize and destroy the old heredity, but we also know why the new heredity is unstable, and what we must do in order to fix it in the desired direction.
If seeds of plants possessing a young and as yet not very stable heredity were to be put into the hands of the Morganist‑Mendelists, they would simply ruin the whole thing because of their disregard for the scientific Michurin approach to plants. And having done so, the Morganists would say: We took your seeds for testing and failed to obtain good results. Consequently, your claim that directed alteration of heredity can be induced is just idle talk.
It is necessary to know not only how to destabilize heredity but also how to fix the young heredity in the desired direction. For this it is necessary to know how heredity is constituted and then to provide the conditions favouring development in the requisite direction. Once we know this, the seeds of the second generation will possess a more stable heredity, the seeds of the third generation an even more stable one, and so on. And seeds of the fourth and fifth generations may even be handed over to the Morganists, who, desire it as they may, will no longer be able to spoil our work, to reverse the plant's course of development.
Research work in the field of variation by the numerous followers of Michurin, coupled with a study of heredity, has brought us to the following, what we think important, conclusion: the environmental conditions that heredity demands for the development in the organism of a given property or character are the very conditions that absolutely must have taken part in creating the heredity itself, in creating the heredity of the given property or character.
By basing ourselves on this conclusion, we are in a position to perform interesting experiments of use in practical farming. For instance, we very much need a frost‑resistant winter wheat for Siberia. To develop such a variety it is absolutely necessary to utilize the severe conditions of the open Siberian steppes. These conditions must be made to act on an organism having a destabilized, nonconservative heredity. We are now able to produce such heredity. Hence we are confident that in a short period of time we shall be able to grow winter wheat capable of resisting the severe conditions of the open Siberian steppes.
Why did the winter wheat that Kotov and Shimansky produced from Erythrospermum 1160 spring wheat prove more winter‑hardy than any other winter wheat coming from the Ukrainian steppes that possesses a conservative heredity? Because fairly severe winter conditions helped to shape the heredity of this wheat. These conditions acted on the destabilized heredity of the new wheat in such a way as to incline it to greater frost resistance. If this wheat withstood the severe Odessa winter of 1939‑40, its seeds will undoubtedly be even hardier than those sown in the autumn of 1939.
If we sow this wheat (and analogous kinds which we now have) under the severe conditions prevailing in the trans‑Volga area or Siberia, furnish it with inclement conditions (but, of course, not so inclement as to kill the wheat altogether!), we shall thereby force the young heredity in the direction of still greater frost resistance.
The experimental work of the followers of Michurin makes it fully possible to convert the inordinately conservative heredity of an organism into an extremely unstable heredity—and this cannot but make us happy.
A person who does not know what heredity is built up from and how it is built up cannot do anything with an organism possessing an unstable heredity. But for people who know what heredity is built up from and how it is built up, organisms with a shaky, unestablished heredity constitute veritable gold mines. We shall subject these organisms to harsher and harsher conditions from generation to generation, shall subject them to severe cold (but, I repeat, only to the extent that it does not kill the plants!), and after two or three years of such training, the wheat we obtain will be in no way different from the local plant forms with respect to hardiness.
You might object that on the open Siberian steppes there is no native winter wheat and hence that there is nothing with which the new varieties of wheat could be compared. It is true that in a number of districts there are no local forms of winter wheat. But there are local forms of weeds which developed under Siberian climatic conditions and fear no frost whatever. Once we know what heredity is built up from and how it is built up, we can make use of this knowledge to train wheat in such a way as to develop in it a winter‑hardiness in no way inferior to that of the local weeds.
First published in 1940