Heterosis in Relation to Development in Upland Cotton, Gossypium hirsutum L.1

The primary objective was to examine hybrids and their parents throughout their life span to detect the onset of heterotic behavior and its cumulative effect. Four single‐cross hybrids of Upland cotton, Gossypium hirsutum L., and their parents were studied. No heterotic effects were detected during the embryonic stage of development. Neither did hybrids appear to be any more vigorous than their parents during the first 7 days of seedling growth following germination. The first significant divergence of hybrids from their parents was recorded at approximately 6 weeks after planting. Relative rates of dry matter production continued to diverge for a period of about 3 weeks and then proceeded at comparable rates in both parents and hybrids to maturity. Hybrids thus maintained their vegetative superiority throughout the period of fruition with the result that hybrid plants were larger than parental plants and produced a greater yield of fruit.