The project consisted of a laboratory phase and a field phase. For the laboratory phase several chemicals were screened for their potential in decreasing transpiration. Because transpiration is water evaporation from the stomata of plant leaves, chemicals which partially close the stomata will reduce transpiration. The closure of the stomata may also reduce CO2 diffusion into plant and thus may reduce photosynthesis and crop yield. Measurements of both photosynthesis and transpiration were made on plants treated with selected chemicals. Several chemicals appeared promising. For the field phase two sensitive weighing lysimeters were constructed and various atmospheric sensors assembled on a 5-acre site about 2 miles southwest of Manhattan, Kansas. During the summer of 1970 sorghum and soybeans were planted on this site and the evapotranspiration from these Crops Characterized. A model for evapotranspiration based on the resistance to vapor diffusion of a single leaf was tested on an hourly basis. (Author)