Wheat is the principal crop of agriculture in Kazakhstan. Its cultivation area amounts to approximately 20 million hectares, of which more than 16 million hectares are planted with spring wheat. Consequently, the solution to the republic’s grain-supply problem depends primarily on the production of spring wheat. The Party and the State have planned the further intensification of agricultural production, with the aim of increasing both yields and their stability. As was specifically emphasized at the July Plenum of the Central Committee of the CPSU in 1978, grain production remains the key link in agricultural development. The task is to consolidate and expand existing achievements, exceed the grain-production targets of the current Five-Year Plan, and during the Eleventh Five-Year Plan raise the average national grain yield to 20 centners per hectare. In addressing these objectives, increasing the productivity of spring wheat cultivated in Kazakhstan and improving its varietal composition are of enormous importance. Since the cultivation of virgin and fallow lands began, wheat production in northern Kazakhstan, especially spring wheat production, has risen significantly. Kazakhstan has become the second breadbasket of the Soviet Union. However, the insufficient drought resistance and relatively low productivity of spring wheat continue to limit increases in its total yield. In many spring-wheat-growing regions of the republic, drought causes substantial crop losses. Sharp rises in summer temperatures accompanied by hot, dry winds under intense solar radiation also reduce yields. Yield losses are particularly severe when soil drought and atmospheric drought occur simultaneously. The problem of wheat drought resistance is one of the most urgent issues in modern biology. Numerous studies, both domestic and foreign, particularly in recent years, have been devoted to drought resistance during plant ontogeny. Despite the considerable attention paid to this issue by biologists and crop-production specialists, many questions remain far from resolved. Among these are the nature of drought resistance in spring wheat, methods for diagnosing heat and dehydration tolerance, and effective means of enhancing this stability. Observations demonstrate that different spring wheat varieties, depending on their origin, developmental stage, and physiological condition, differ in their capacity to tolerate adverse environmental conditions and thus possess different levels of resistance. Agronomic and agrochemical measures do not always succeed in increasing plant resistance to unfavorable conditions. As I. V. Michurin stated, in such cases, “the variety determines the success or failure of the undertaking.” Among the various measures aimed at maximizing grain production, the introduction of high-quality varieties adapted to specific local environmental conditions plays a particularly important role. Scientists in Kazakhstan have achieved significant success in this area. Owing to the work of breeders such as V. P. Kuzmin, N. L. Udolskaya, L. V. Pimenova, Ya. K. Bechek, A. K. Gorbéks, and others, breeding methods have been developed for different regions of the republic, and high-yielding varieties well adapted to local conditions have been produced. However, at the present stage of development of the biological and agricultural sciences, further variety improvement increasingly depends upon a deeper understanding of the laws governing plant development and productivity. It is now generally recognized that, in addition to breeders, geneticists, agronomists, plant physiologists, biochemists, and specialists in other biological disciplines must work together in variety development. Within this integrated effort, plant physiologists should play an especially important role, since their task is to reveal the characteristics and interrelationships of plant life processes. The challenge facing breeders is to create varieties possessing a high degree of resistance to both soil and atmospheric drought. To achieve this, it is first necessary to identify traits associated with water relations and other physiological indicators, determine their significance and the desired direction of their modification, and ensure their incorporation into breeding programs. For both breeding and the ecological-geographical zoning of varieties, it is of great value to identify the adaptive significance of physiological functions that characterize wheat cultivars under specific environmental conditions. At the same time, stronger links between physiology and plant breeding must be developed so that breeders may receive practical guidance based on biological type, developmental stage, organ function, and specific traits, thereby enabling the physiological improvement of crop varieties. Consideration of the general laws of ontogeny is of exceptional importance for both plant breeding and the practical cultivation of wheat. It is well known that environmental conditions strongly influence physiological processes, particularly in regions characterized by climatic instability and frequent drought. A comprehensive investigation of the changes in various characteristics of spring wheat during ontogenetic development will contribute to revealing the biological potential of this crop, regulating its growth and development processes, and ultimately controlling the formation of yield. Naturally, the issues discussed above do not exhaust all the biological problems associated with spring wheat. A number of other questions are of great importance, including the physiology of mineral nutrition, irrigation, and the use of growth regulators and herbicides. In Kazakhstan these important topics remain insufficiently studied and require substantial effort and detailed investigation by experimental researchers. On the occasion of the twenty-fifth anniversary of the cultivation of virgin and fallow lands, we considered it appropriate to summarize the results of our own studies and those of our collaborators on the physiology of spring wheat conducted during this period. Together with findings from other branches of the biological sciences, these studies have illuminated the factors determining the stability and productivity of spring wheat under the unfavorable climatic conditions of Kazakhstan. The authors believe that a comprehensive review of these issues is necessary not only for evaluating achievements already made but also for identifying future directions of research in this constantly relevant field. In order to explain and examine certain questions in greater depth, the present monograph also makes extensive use of materials on wheat physiology accumulated in both domestic and foreign scientific literature. The authors pay tribute to the outstanding achievements of V. P. Kuzmin, Hero of Socialist Labor, Academician of the Academy of Sciences of the Kazakh SSR and the All-Union Lenin Academy of Agricultural Sciences. His persistent efforts to bring physiological research into closer alignment with the specific needs of plant breeding exerted a decisive influence on the development of this work. The authors also express their sincere gratitude to the colleagues and fellow researchers who participated in the experiments and contributed to discussions of a number of the ideas reflected in this book.