Litoyp: LEAF WATER IN GOSSYPIUM 19 
tions, now possible by the use of the method I have described 
above, and with reference also to F. Darwin’s* verification in 
cooperation with Pertz, by means of the porometer, of his earlier 
work on the temporary opening of stomata during wilting, I 
measured by weighing the rates of transpiration of a piece of a 
cotton plant during wilting. After the cutting off, the cut was 
greased and the piece was suspended on a balance, the loss of 
weight being determined at intervals of several minutes, beginning 
at 7.22 when the stomata were open but had not reached their 
maximum. The leaves were turgid. The figures obtained (TABLE 
X1) show that between 8.02 and 8.07, following a steady fall in the 
rate, there was a temporary rise, and while this was very small 
when compared with Darwin’s data, it may be a phenomenon 
comparable with that observed by him. However, that the 
stomata open after wilting sets in still appears doubtful to me. I 
have watched microscopically the stomata of the cotton, in addi- 
tion to those of several other species, during the wilting period, 
beginning with the partly as well as fully opened condition, and I 
have never observed any such movement. There is at first no 
change. As wilting sets in, closure commences and proceeds 
steadily till complete, and I have observed no subsequent opening. _ 
Obviously further investigation is required to throw light on these 
differences. 
CONCLUSIONS 
In the foregoing paper a method for the direct observation and 
measurement of stomata im situ is described. The method is 
' adapted to field work by night and by day. 
_ Leaf water, stated in percentage of dry weight, was found to 
vary in the cotton plant under usual conditions between 318 and 
220 per cent. On the day of observation the minimum leaf water 
content was reached at the 14 hour or thereabouts. This reduc- 
tion represents a net loss as shown by the determinations made 
relative to unit area and, therefore, with quantitative regard to 
dry weight. 
The amount of loss of leaf water when thus determined is from 
7 to 15 per cent. on the initial amount at sunrise, under the condi- 
Darwin, F., and Pertz, D. F. M. Ona new method of estimating the aperture 
of stomata. Proc. Roy. Soc. B, 84: 136-154. I9II. 
