Mason . — Growth and Abscission in Sea Island Cotton . 473 
growth-rate is inevitable as a result of the augmented water strain which 
attends the more rapid ascent of sap during the hours of sunlight. The 
ratio between the day and the night growth-rate is also shown in the figure ; 
this is of interest in that it demonstrates that the daytime growth-retardation 
evaporation, and rainfall. Gp. II. 
became more marked as the daily growth-rate approached zero. This is 
possibly the result of a decrease in the water-supplying power of the soil, 
but the operation of internal factors is not excluded. In view of these 
results it becomes comprehensible why, under the conditions in St. Vincent, 
little or no shedding can be traced to pronounced saturation-deficits in the 
plant body. 
The Growth-rate of the Boll and Fertilization. 
In an earlier section it was pointed out that the young boll is especially 
liable to be shed when about seven days of age. This in the past has 
sometimes been considered indicative of a factor inhibiting fertilization (1). 
It would seem impossible normally to associate this with unsuccessful 
pollination, for the interval elapsing between the reception of the stimulus 
and the completion of abscission is under field conditions only about five 
days. Moreover, it will be remembered that the more constant cause of 
shedding appeared to be associated with conditions which tended to retard 
the growth of the plant as a whole rather than with the influence of day- 
time rain on individual flowers. It seems legitimate to infer that the 
metabolic transformations which precede abscission, and which probably in 
L 1 
