Litoyp: LEAF WATER IN GOSSYPIUM 21 
understood causes) by the increase in dry weight. Two series in 
Arizona gave increases of 24 and 32 per cent. for 8 hours. In 
Alabama, with the exception of one series of old leaves in which 
there was no apparent change in weight, the increases ranged from 
6 to 25 per cent., the latter being one instance out of a total of 
seven series. Whatever may be said of increase in dimensions, 
therefore, it remains the fact, that in spite of the hot unmodified 
Arizona sun shining throughout continuously cloudless days in 
August, more energy in the form of carbohydrates was made 
available than in the similar periods in Alabama. It is proper, 
however, to recall that the leaves studied in Arizona were of fuller 
development, while those in Alabama were either rather young 
(10-15 cm. transverse measurement) or overmature. 
It is obvious that it will be of great interest to make careful 
measurements of growth, as indeed of other functions, for com- 
parison with those of Balls in Egypt. 
The stomata are practically closed at night, but nevertheless 
show a tendency to open during the early morning hours.* The 
more obvious daily opening begins at about 6.30, in Alabama in 
September, and the maximum is reached at about 8.30 or 9, after 
which’ closure progresses until 11 or somewhat later. A con- 
comitant and appreciable wilting takes place, correlated with the 
reduction of leaf water. During wilting there appears to be no 
“temporary opening’”’ of the stomata, although I have observed a 
measurable but not very marked rise in the rate of transpiration 
about a half hour after wilting starts in, followed by a sudden 
reduction of rate. 
*Lloyd,F.E. The physiology of stomata. Carnegie Inst. Wash. Publ. 82. 1908; 
arwin, Francis, and Pertz, D. F. M. Ona new method of estimating the aperture 
of stomata. Proc. Roy. Soc. B. 84: 136-154. I9I1I. 
