In recent years there has been renewed interest in the role of the environment in eropimprovement research. A basic program of research in genotypeenvironment relationships was begun at Substation No. 8 of the Texas Agricultural Experiment Station at Lubbock, Texas, in 1959. Although this research is still in the preliminary stages, several practical leads have already been developed. For instance, it has been found that, at a given location, date of planting had a greater over-all effeet on yield than did variety. The data show also that the performance of a given variety depends on the accuracy of the estimates of the length of the growing season and the number of days of "optimum" temperatures that will oecur during the growing season. A method of predicting performanee of various varietal types by estimating "heat units" during the growing season has been devised. Since date of planting is a major factor in determining the length of the growing season, it also contributes importantly to the development of "heat-unit" estimates. Experiments at the Lubbock station have shown that, if planting can proceed during the "optimum" period in the spring, certain varietal types should be planted. On the other hand, if, beeause of adverse weather, hail damage or some other condition or circumstance, planting must be delayed beyond the "optimum" period, other tested varietal types should be planted.