Transpiration of plants accounts for a tremendous amount of water utilization under both irrigated and dryland conditions. Much attention has been given to measuring this loss, but relatively little attention has been given to controlling this loss by manipulating plant responses to different conditions of water availability, or to increase their efficiency in water utilization. Objectives of this study, from July 1, 1969 to June 30, 1972, were to gain an understanding of plant biophysical mechanisms and responses by: (1) analyzing the biochemical effects of internal water stress on physiological processes such as photosynthesis and respiration, and (2) analyzing the mechanisms by which plant water potentials and water use are controlled or influenced by the plants. 'Harvester' snapbeans (Phaseolus vulgaris L.) were used for these investigations. (Author)