Feb. 28,1916 
Relation of Stomatal Movement to Infection 
1027 
opening in both places occurred about 5 a. m., and in the humidity box 
the opening on the lower leaf surface exceeded that on the upper, this 
relation remaining uniform throughout the day. This tendency is also 
indicated in figure 3 in the greater stomatal opening of the lower over 
the upper leaf surface in the humidity box. These observations in gen¬ 
eral agree with the findings of other investigators. Darwin (2) found 
that the stomata on the lower surface often opened earlier and remained 
open longer than those on the upper, though this was not always true. 
He believed that the difference in the opening was due to illumination 
rather than to any inherent distinction between the stomata. Livingston 
and Estabrook (5) found in the study of the stomata on several different 
Fig. 5.—Stomatal pore widths on mature leaves kept under different relative humidities in a humidity box 
(H. B.) and free in the greenhouse (G. H.) at Rocky Ford, Colo., on June 3, 1913 (Table VII). 
kinds of plants that those on the upper surface open and close more 
rapidly and close more completely than those on the lower. Lloyd (7) 
observed with cotton that— 
The initial opening on September 30, 1911, occurred about 6.30 a. m., from which 
hour on a progressive opening movement was followed, the stomata of the lower 
surfaces opening somewhat in advance of those of the upper, though some exceptions 
to this appear. 
Again, on June 3, after all the beds in the greenhouse had been watered 
on the preceding evening and the humidity box placed at that time over 
a portion of the plants for the test, the same general results were obtained, 
in that the stomata opened wider and remained open longer in the humid¬ 
ity box with higher humidity active for a longer period than in the green 
house (fig. 5). During this test the stomata in the greenhouse remained 
open during midday till about 3 p. m., owing probably to the fact that 
