56 THE ROYAL SOCIETY OF CANADA 
pointed out by Hannig? difficult to determine. If this period is re- 
garded as delimited by the earliest evidences of histological activity 
and the condition when final separation is possible, it may be, for young 
bolls, less than four hours. This was determined by injuring bolls 
sufficiently to ensure practically 100% abscission within 24 hours. 
In 16 hours there was no evidence of histological activity, while 4 
hours later the process was practically complete. The reaction 
period for larger bolls has not been determined, but as from one to 
five cell-divisions may take place and as the physiological activities 
of the abscission cells have to overcome the resistance of variously 
indurated membranes, the period in question must be longer? 
SHEDDING AND THE ENVIRONMENT 
In order to correlate the fluctuations in the march of shedding 
with changes in the environmental factors, it was necessary to deter- 
mine the length of the abscission period (the whole period between 
the imposition of the stimulus and the final completion of the response) 
in the field, following a variety of stimuli. This was done (a) by the 
analysis of the data obtained by tracing the history of 579 flowers 
which ultimately were shed; and (b) by experiments ad hoc. These 
experiments consisted of inflicting injury in various degrees to squares 
and to bolls; of removal of portions of the root systems; of intercepting 
the water-current to the plant as a whole or to the bolls in particular 
by the excision of tissues in suitable places; of prejudicing fertilization 
by applying water to the pollinated stigmas, and correlating the results 
in shedding so obtained with those following rain at various times of 
the day, so far as occasion offered. 
Conclusions from experiments. The results of injury to squares 
and bolls show that the abscission period may be as brief as 24 hours, for 
the youngest bolls, to three days for bolls 25 mm. in transverse dia- 
meter. 
The observed periods for all kinds and sizes of squares and bolls 
(30 mm. of less) were six days or less. Bolls larger than 30 mm. 
transverse diameter are seldom shed in the field. In view of the dras- 
tic treatment it may be inferred that these are responses of maximum 
rapidity at the temperatures which prevailed, these corresponding to 
the usual summer field temperatures. It was found that squares 
do not shed quite so readily as small bolls, the reason for which is 
1Hannig, E. Untersuchungen über das Abstossen von Blüten u. s. w. Zeitschr. 
f. Botanik. 5: 417-469. 1913. 
2Lloyd, F. E. Abscission. Ottawa Naturalist. 28: 41-52. June-July; 
61-75. Aug.—Sept. 1914. 
