14 Lioyvp: LEAF WATER IN GOSSYPIUM 
the succeeding night. They open slowly after sunrise, but more 
rapidly after the sun strikes the leaf at about 7, attaining the 
maximum opening at 9, but thereafter closing steadily in spite of 
brilliant illumination. So far as I am aware this is the only record 
of the behavior of the stomata in cotton. 
The measurements given in TABLE x, made microscopically 
and at the same time by two observers, Mr. C. S. Ridgway and 
myself, in the manner earlier described, correspond in a rather 
striking way with Balls’ conclusions, just indicated. Each for- 
mula represents the minimum and maximum width of the 
stomatal pores on the upper and under sides of the same leaf. 
When a very few stomata displayed extreme dimensions, these 
are enclosed in parentheses. It may be regarded that these would 
on account of their small numbers affect but little the general 
diffusive capacity of the stomata taken as a whole. 
It is evident that during the night and until 6.20 there was no 
measurable opening movement. This must not be taken to mean 
that all the stomata were entirely closed. TABLE IX gives 
stomatal dimensions from preparations made by the alcohol 
method, in which it is evident that some opening in a few stomata 
may be observed at any time during the night. The initial opening 
on September 30, 1911, occurred about 6.30, from which hour on a 
progressive opening movement was followed, the stomata of the 
lower faces opening somewhat in advance of those of the upper, 
though some exceptions to this appear, as at 7.50 and 8; while 
Livingston and Estabrook* found, in several kinds of stomata, 
that the upper close and open more rapidly or close more com- 
pletely than the lower. The maximum average pore width was 
attained during the period between 7.45 and 9, though the widest 
openings were seen at 8.20. Because of the extreme sizes of 
opening then noted, leaves of similar size and exposure were 
examined to verify the observation, but they were no more seen 
during the morning, except in one instance an hour later. The 
closing phase was at once entered upon, but it is evident from 
the figures that this movement was less uniform in all the leaves 
taken together than the opening. This may be readily understood 
* Livingston, B. E., and Estabrook, A. H. Observations on the degree of 
stomatal movement in certain plants. Bull. Torr. Club 39: 15-22. 12 F 1912. 
