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.

This study was carried out during the two successive seasons 2014/2015 and 2015/2016 at the experimental farm of Sakha Agricultural Research Station, Kafr El-Sheikh, Egypt. Eight bread wheat (Triticum aestivum L.) cultivars and lines, differing in their earliness were used as parents and evaluated with their 28 F1's under optimum (29 th Nov.) and late (29 th Dec) sowing dates. The studied characters were earliness, grain yield and its components. significant differences were detected between the two sowing dates and among the studied genotypes in each sowing date and across the two sowing dates. The mean squares of GCA and SCA for most studied characters were significant or heighly significant under both sowing dates. Means of the parents and their crosses were decreased under late sowing date for all the studied characters. The early parents and most of their F1's had the desirable mean values for combining ability and heterosis effects for earliness characters. Moreover, the parents Giza 171, Misr 2 and Line 1 (late parents) were the best parents for mean performance and general combining ability (GCA) for grain yield and its components in most cases. Four crosses resulting from late and early parents under both sowing dates were the highest ones and could be used in advanced studies for earliness and grain yield potential. The GCA/SCA ratios were more than unity for most studied characters under both sowing dates.

The effect on cross pollination of four directions and six distances from the marker variety in Egyptian cotton was investigated. The percentage of cross pollination did not differ appreciably in the different directions but there were significant differences in cross fertilization among the six distances. A linear relation was observed between cross pollination per cent and distance up to 8 • 8 m. from the marker variety. Implications of these findings on various aspects of cotton breeding methodology are discussed.