The authors have studied the physiological life span of leaves in a confectionery sunflower variety 'Three Brows' and a corn hybrid 'Jing Hybrid Number' used as a check, with intention of establishing indicaton for control of leaf growth and prwenting a premature senescence of sunflower leaves. In the sunflower variety, the 35th leaf was found to have the longest physiological life span of 58.4 days; the 44th leaf had the longest life span after flowering, 45.8 days. The average period of physiological activity of leaves after the stage of flowering was 29.0 days, i.e., 62.5 % of the entire physiological lifetime. The respective figures for the corn hybrid were: the 15th leat - 94.9 days; the 20th leaf- 67.1 days; 53.2 days or 87.7%. It is pointed out that grain yield could be further increased by prolonging the physiological life span of leaves after the stage of flowering which would promote the process of grain filling, increase grain weight and decrease the percentage of hulls.