468 Mason . — Growth and Abscission in Sea Island Cotton. 
atmometers were dislodged by the wind ; evaporation was, however, as may 
be inferred from the amount of daytime rain, very small on the 8th, and 
also on the 9th. The tardiness in the rates of recovery of the growth-rate 
at this time was partially due, no doubt, to root injury sustained as a result 
of the wind, but was mainly, as reference to Fig. 4 indicates, due to the 
normal decline in the growth-rate occasioned by the augmentation in 
the number of the developing fruits. This conclusion is sustained by the 
rapidity with which some young plants in a neighbouring plot recovered. 
The plants were not measured on the 8th, so that the growth-rates for this 
and the following day have been taken as the mean of the two-day 
period. 
Referring again to Fig. 8, it will be seen that a wave of bud-shedding 
occurred 4-5 days, and of boll-shedding 5-6 days after September 8. 
The shedding waves which took place on the 7th, 8th, and 9th of the same 
month commenced six days later than the retardation in the growth-rate 
of the main axis which occurred on the 1st. The comparative absence of 
shedding during the earlier part of the period is not only ascribable to the 
paucity in the number of flower-buds and bolls, but also to their very slight 
liability to undertake the abscission response at this period. 
It will be evident that no definite relationship can be traced between 
the daily fluctuations in the growth-rate of the main axis and the amount 
of shedding which ensued. The results, nevertheless, indicate a strong 
probability that the same external factors — to wit, daytime rain and low 
rates of evaporation — which cause a retardation in the growth-rate during 
the earlier periods of the plant development, are also responsible for the 
extensive shedding of bolls which occurs during the later portion of the 
flowering period. It would follow, if this view is correct, that the same 
internal factors are the cause of both phenomena. As yet the relative 
importance of these various internal factors cannot be diagnosed, for day- 
time rain and the reduction in light intensity which accompanies low rates 
of evaporation might retard not only the rates of carbon assimilation, but 
would also lead to large turgor pressures (possibly attended by incipient 
guttation), which would limit the supply of electrolytes normally translocated 
with the transpiration current ; the net result would presumably be a check 
in the supply of elaborated food. It is also conceivable that the transloca- 
tion of assimilates might be inhibited by the augmentation in the turgor 
pressure. 
The difficulty encountered when the attempt is made to ascertain 
whether or no the extent of the daily fluctuations in the growth-rate is 
directly related to the amount of boll-shedding arises of course from the 
fact that throughout the period of greatest susceptibility to shedding the 
growth of the main axis has practically ceased. At first sight it might 
appear feasible to bridge this gap by determining whether the amount of 
