Growers and investigators of sorghum (Sorghum vulgäre Pers.) generally have observed the small size of seedlings and the relatively slow early growth of the plants, as compared with those of corn, even when grown under optimum conditions. Measurements of the growth of sorghum plants at some stages doubtless have been made previously, but curves showing the trend of this slow early growth have not been found in the literature. In 1930, N. V. Kanitkar, then soil physicist of the Poona Agricultural College, Poona, India, while visiting the United States, showed the junior writer an unpublished growth curve of sorghum based upon data he had obtained in India. This curve was of the unbalanced sigmoid type, having a long gradual slope during the first several weeks of the period, that depicted strikingly the slow early growth and rapid later growth of sorghums. It seemed desirable to the writers to investigate this problem in the United States and if possible to determine the cause of this unbalanced trend in growth rate. The experiments were conducted by the senior writer. Sorghums are of tropical origin and usually grow slowly at the cool temperatures that frequently occur after relatively early planting in the Northern States. The sorghums in the experiments reported here, however, were planted in June and July under conditions of high temperature and irrigation in southern Arizona, which favored rapid germination and early growth. Thus unfavorable environmental conditions that might have retarded early growth were largely eliminated from consideration as a causal factor in the growth trend.

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