Relationship of Seasonal Trends in Carbohydrate and Nitrogen Levels and Effects of Girdling and Spraying with Sucrose and Urea to the Nutritional Interpretation of Boll Shedding in Cotton.

The shedding of young cotton bolls has for many years been widely attributed to nutritional relations; insufficient carbohydrate and nitrogen supplies have most often been thought of in this connection. This view of the cause of boll shedding is possibly quite old, but the first reference with which the writers are familiar is that of MASON (20) in 1922 in which he said that both the cessation of growth of the main axis and the augimiented susceptibility to shedding could be attributed to a correlation factor which tended to deflect the supply of elaborated food from the apical part of the plant to the fruit developing on the basal fruiting branches. In 1934 MWASON and PHILLIS (21) wrote that the bolls drain the vegetative plant of its food materials, the leaves yellow and fall off as nitrogen is drained away, and as the strain increases the flower-buds and bolls themselves are starved and shed. In 1931, one of the present writers (2) stated that the nutritional dominance of bolls over the vegetative growth of the cotton plant had frequently been observed to inhibit boll setting and terminal bud and branch development. Eaton, in a section of a Field Station report by KING and LOOMIS (17) stated that a very close relation exists between the rate at which organic products are made available by photosynthesis and the number of bolls that the cotton plant retains. None of the foregoing conclusions was supported by original analytical data but it was known from earlier work that the nitrogen content of vegetative parts of the cotton plant declines with the advance of the summer. 1\ASONN (20) had found that the removal of all leaves caused a prompt shedding of nearly all young bolls carried by Sea Island cotton plants, and EATON (2) had found that when previously set bolls were removed from Upland plants these were replaced within a matter of 10 days with new bolls. HAWKINS et al. (15) lfleasured the trends in carbohydrate levels in cotton plants throughout a summer and concluded in 1933 that the percentage of shedding is regulated by the amount of plant food available for the development of the young bolls. The conclusions drawn by WADLEIGH (23) in 1944 were that Nhen developing ovules in cotton bolls already set have sufficiently depleted nitrogenous or carbohydrate reserves to a level of inadequacy for further ovule development, the additional young bolls abscise because of ovule abortion; after