474 Mason. — Growth and Abscission in Sea Island Cotton. 
some way inhibit fertilization, or, what is more probable, inhibit the stimulus 
to fruit development, are especially liable to be initiated some days after 
rather than during the open flower stage. The results of some measure- | 
ments of the growth-rate of the bell, which seem to bear on the point, will 
now be considered. 
The two graphs in Fig. n represent the daily growth-rates of forty-two 
bolls, thirty-eight of which completed development and four of which were 
shed on the seventh and eighth days after the open flower stage. The 
measurements were made at 10 a.m. daily, and represent the daily rate of 
increase in the diameter of the boll in thirty-sixths of an inch (0*71 mm.). 
The growth of the thirty-eight 
bolls which completed develop- 
ment, it will be seen, falls into 
two distinct stages. The first, 
which terminated on the 5th day, 
is one of increasing growth, where- 
as the second stage, which follows 
it, is suggestive of the curve of 
autocatalysis, that is to say that 
the rate is initially slow, increases, 
and then declines. Comparison 
with the growth of the four bolls 
which were shed on the 7th and 
8th days shows that the first 
stage is essentially similar in both, 
but that in the latter recovery 
failed to occur. It is certainly 
very suggestive that the period 
which other considerations point 
to as the period of greatest 
susceptibility to the stimulus which initiates abscission should be also 
one of growth-retardation. It will be remembered that the period of 
greatest susceptibility to shedding did not occur until after the inhibition 
of growth in the main axis, and that the same external factors which were 
associated with a retardation in the growth-rate of the main axis also 
preceded augmented rates of shedding. 
The next point which calls for comment is the role played by fertiliza- 
tion. Balls, it will be recalled, has pointed out that fertilization in the 
cotton-plant is normally completed within thirty hours after the opening 
of the flower, i. e. by the afternoon of the following day. If recovery in the 
growth-rate on the fifth or six days after the open flower stage is dependent 
on fertilization, it is an interesting fact that a delay of 4-5 days should 
occur between the completion of fertilization and the transmission of the 
Fig. 11. Showing the two stages in the 
growth of a boll. 
