464 Mason. — Growth and Abscission in Sea Island Cotton. 
follow that the incidence of any external growth-retarding factor would 
lead to a check in the rate at which elaborated food was being produced, 
and the consequent reduction in the supply of assimilates might well furnish, 
either directly or indirectly, the stimulus for augmented rates of shedding. 
The hypothesis is supported by an experiment made by Ewing ( 2 ) in 
Mississippi, in which it was found that the daily removal of all the flowers 
almost doubled the amount of flowering, but that the destruction of one- 
half of the flowers produced during the last six-tenths of the flowering 
period led to a scarcely appreciable increase in the flower production ; it 
did, however, almost completely offset the natural tendency to shedding. 
Presumably the supply of assimilates liberated as a result of the suppression 
of the fruit development is expended in further flower production, but in 
the presence of a number of growing bolls any assimilates available are 
mainly employed in furthering their development, and thereby reducing 
their liability to be shed. The shedding of a certain proportion of the 
flower-buds and young bolls is probably inevitable, and need not, therefore, 
be viewed with concern. 
Environmental Factors and Boll-shedding. 
The difficulties encountered when the attempt is made to trace a 
quantitative relationship between the percentage of young bolls eliminated 
by abscission and the causative external factors, arise on the one hand from 
the complexity of the processes which determine abscission in the plant 
body, and on the other from our inability, as yet, to measure many of the 
environmental factors which directly influence the metabolism of the plant. 
To these difficulties must be added those introduced by the biological 
environment, fungous and bacterial diseases, and insect depredations. 
The rates at which boll-shedding occurred during the later portion of 
the flowering period are shown for each of the groups in Figs. 6 and 7 
respectively. In the first group, it will be remembered that the number of 
bolls which were shed on Sundays was not directly determined, and that 
one-third of Monday’s quota was credited to these days, which are indicated on 
the graphs by the solid black circles. A word of explanation is also needed 
concerning the environmental factors of which records were kept, and the 
method of their presentation. 
Evaporation from the Livingston spherical atmometers, both black and 
white, was measured daily in duplicate at 9 a.m. ; the difference is 
represented in the figures as ‘ Evaporation due to solar radiation ’, whereas 
‘ Evaporation ’ refers to the total evaporation from the black atmometer. 
‘ Daytime rain ’ indicates the amount of precipitation which occurred between 
9 a.m. and 3 p.m. ; it therefore represents the rainfall occurring during the 
hottest part of the day. A daily record of the temperature, both of the 
subterranean and aerial environments, was also kept, but, owing to the small 
