Lioyp: LEAF WATER IN GOSSYPIUM 15 
when it is appreciated that the stomata of cotton are quite sensi- 
tive. I observed, both in Alabama and in Arizona, that at the 
same hour a leaf in the shade and one in the sun were physio- 
logically antipodal in this regard. Thus, at 8.30, August 24, at 
Tucson, Ariz., the stomata of a leaf in the shade were closed 
both above and below, while those fully exposed to sunlight on 
another leaf were 0-10u wide above, and 2-44 ‘below. Similar 
conditions are displayed by the leaves observed at the 1o hour, 
TABLE x. At the same hour it was noted that the stomata 
near the apex of a leaf were closed while those near the base were 
open, a condition readily understandable if wilting is progressive 
from the apex of the leaf downward. 
As between young and old leaves, the latter being still physio- 
logically active, it is not clear that there was a more pronounced 
tendency in one kind than in the other either toward opening or 
closing, nor that the leaves near the base of the plant were more 
favorably placed than those three feet above, at or near the top. 
Indeed, that the upper leaves close their stomata less early than 
those near the base seems indicated, and this is in harmony with 
Rringsheim’s findings,* who believes that the apical parts of the 
plant withdraw water from the older, the result of more rapid 
transpiration from the younger organs. 
The data of the table which we have been considering must 
be regarded, however, rather as an indication of the usefulness of 
the method of microscopical observation in the field after the 
manner already described. The measurements were taken rather 
at random, and as the plants were nearing the end of their career, 
the larger leaves being somewhat passées, while the young were 
from ‘‘second growth” shoots, at the tops of the plants. Their 
general indications, however, I believe, may be relied upon, 
namely that the maximum opening of the stomata is reached 
at about 8.30 in the morning. It has been the invariable experi- 
ence of three observers during the season of IgII at Auburn, and 
of one of them at Tucson, that wilting of the leaves becomes first 
evident at about this hour or somewhat later each day, when sun- 
light conditions prevail. The reduction of leaf water leading to 
*Pringsheim, E. Wasserbewegung und Turgorregulation in welkenden 
Pflanzen. Jahrb. Wiss. Bot. 43: 89-144. 1906. 
