High population densities have been proposed as one way of achieving earlier maturity in cotton (Gossypium hirsutum L.) by increasing the potential number of early fruiting points. But competition among closely spaced plants may adversely affect initiation and set of fruit. Theoretically, competition can be reduced by improving the uniformity of plant distribution. A year field study was conducted to determine the morphological and agronomic reactions of cotton to intraspecific competition over a wide range of plant populations within equidistant spacing configurations. Response to equidistant plant spacing was studied using two genotypes of upland cotton (Gossypium hirsutum L.) with contrasting plant types and five population densities ranging from 38,750 to 620,000 plants/ha in patterns where distance between plants within the row equaled the distance between rows. Vegetative and fruiting components were measured and dry weight determinations were made after destructive fractionation at three harvest dates. Yield, earliness, and fiber quality data were accumulated from weekly harvests of mature bolls. As plant population increased, dry weight per unit land area of all plant components increased except vegetative branches, which decreased. Leaf area index and the number of nodes to the first fruiting branch also increased with higher populations. A smaller, more compact plant developed as plant density increased, which was indicated by reductions in plant height, stem diameter, and number of branches. Boll size, number of seed/boll, seed index, and lint index were all reduced as plant spacing decreased. Retention rate of fruiting forms was apparently much lower in the very high plant densities. Population levels of 79,000 and 155,000 plants/ha were earlier maturing and produced higher lint yield than population levels on either side of this range. These results generally agree with those of investigations of cotton spaced in 1‐m rows. There was no evidence that high population densities in equidistant spacing patterns improve earliness or yield.

Five cotton varieties were grown in the field under four different night temperature regimes (10, 15, 20, and 25 C). The influence of temperature on the rate and extent of fiber elongation was studied. Temperatures below 20 C reduced fiber length; and generally, the reduction was greater in varieties having the longer fibers. Lowering night temperature increased the fiber elongation period and slowed the fiber growth rate. The temperature coefficients of elongation indicated the rate of elongation for all varieties was extremely temperature‐sensitive up to 15 days age. Beyond 15 days age, however, the coefficlents of elongation quickly approached one, indicating temperature independence.

We studied the stability, adaptation, and yields of several diverse cotton (Gossypiutn hirsutum L.) cultivars that had been grown at several locations in one or more of three, 3‐year periods of testing. We used as environmental indexes the mean lint yields of three “standard” cultivars that were common to all tests. The yields of the remaining cultivars were regressed upon these indexes. The regression coefficients (6 values) were used as measures of adaptability, and the coefficients of determination (r2 values) were used as measures of stability. Analyses of variance of lint yields also were computed.In comparison with the three standards, most of the other cultivars were adapted to all environments (b = 1.0), and all but one were stable. However, there were several significant yield differences among the cultivars within each of the three periods of testing. Thus, yield level was the most divergent parameter measured, adaptation was next, the stability was the least divergent. Because we found significant differences among commercial cultivars in both adaptation and stability, we believe that the use of these two parameters in conjunction with yield would be of significant benefit in breeding material evaluation.