204 
Journal of Agricultural Research 
Vol. XXV, No. 4 
show that the bolls produced during the late flowering period were 
actually slower in maturing than the early bolls. The mean number of 
days between bloom and open boll for flowers opening from July 21 to 
July 26 was found to be 42.57 days, while that for bolls set from August 
3 to August 8 was 44.55 days. A probable error of ±0.068 days and 
±0.23 days, respectively, was obtained on these means. These determi¬ 
nations show that the increase of 1.98 days in the maturation period of 
the later bolls is eight times the probable error of the difference, indi¬ 
cating that it is significant. 
No rain occurred throughout the maturation period of either the early 
or late bolls, and the increase of about two days in the period of matura¬ 
tion of the late bolls may have been due to the checking of plant growth 
by drought. This suggests that boll opening was not due primarily to 
the effect of atmospheric conditions in drying the bolls. Excessive shade 
or moisture, or lower temperature, undoubtedly tends to defer boll 
opening, but under consistently dry conditions a longer interval between 
bloom and open boll in later bolls may be due to a retarding of growth 
processes. It might be expected that drought would result in a pre¬ 
mature opening of bolls, but the results obtained at Greenville did not 
indicate any such effect. Jt is probable, however, that more severe 
conditions would result in premature opening. 
GROWTH OF PIMA BOLLS IN ARIZONA 
Other data on the growth of bolls were obtained from the Pima Egyp¬ 
tian variety at Sacaton, Ariz., in 1921. These records include determi¬ 
nations of the volume, green weight, and dry weight of the growing bolls 
at regular intervals after flowering. 
Table X presents the average volume and weight of Pima bolls as 
determined from 60 boll samples collected at five-day intervals. From 
this table it can be seen that the average Pima boll grows very rapidly, 
reaching its mean maximum volume of 14 cc. at the age of 25 days. 
Even at 15 days the bolls are nearly full size. (PI. 2.) The growth, 
however, as shown by green weight is not so rapid, the mean maximum 
of 13.4 gm. being obtained at the age of 40 days. Measured by dry 
weight, the growth is even less rapid, and the mean maximum of 3.8 
gm. is not reached until 50 days of age. 
It is evident from these data that the average Pima boll Teaches 
its maximum volume in less than half of the period between the dates 
of flowering and opening of the boll. The green weight of bolls attains 
a maximum and then declines before maturity is reached. Growth by 
dry weight gives the best index of progress toward mature development, 
the maximum of dry weight of the average boll being attained at least 
10 days before opening. 
