Influence of Growth "Hormones" on Boll Retention by Cotton Plants

Under climatic conditions of the San Joaquin Valley of California dusting cotton plants during periods of active shedding with 100 p.p.m. of sodium 4-chlorophenoxyacetate and 1000 p.p.m. of naphthaleneacetic acid was without effect on boll retention in both 1947 and 1948. 2. Spraying plants weekly with a 20-p.p.m. solution of sodium 4-chlorophenoxyacetate, in an experiment where naphthaleneacetate and napthoxyacetate were without effect, significantly reduced the number of bolls per plant and the number of bolls per 100 gm. of stems and leaves and caused some increase in vegetative development. 3. The fruiting branches of the cotton plant are in some respects homologous to the inflorescences of other plants-that is, under certain conditions cotton can develop either vegetative or fruiting branches to the exclusion of the other type. Only the fruiting branches produce flowers. Various synthetic-hormone sprays used on various types of cotton and under various conditions did not materially alter the kind or proportions of branches developed. 4. The foregoing data provide little basis for believing that the late-season setting of cotton bolls can be increased by the use of the type of growth-regulating materials employed or for believing that these materials can alter materially the proportions of fruiting and vegetative branches. A florigen type of growth substance might, however, have marked effects. Also, the anti-auxin type of material remains to be studied.