STOMATAL MOVEMENT. 39 
In most instances the majority of the stomata were about the average size. 
A test of the method of selection was made by taking a leaf at random and 
measuring all the stomata included in it. The average was found to be 
practically the same as the one obtained by the first method. Intheopinion 
of the observer the widths given represent very little error, but. where the 
openings were small the lengths could not always be determined accurately. 
Every measurement was made to include equal numbers of stomata on the 
two sides of the leaves. The necessity for the inclusion of the stomata of 
both sides of the leaves in measurements of this kind has been pointed out 
by Livingston and Estabrook.* 
Table 15 contains the results reduced to microns, including the length (1) 
of the openings between the guard cells, the width (w) of the opening, and 
the square root of their products (WJw).t 
A comparison of the curves shows that the method under discussion gives 
approximately the same results as Lloyd’s absolute alcohol method. In 
one respect this method seems to have an advantage over the absolute 
alcohol method, namely, that the guard cells are not subjected to the danger 
of loss of water from evaporation during the interval of transfer from the 
leaf to the alcohol, a factor which might be serious in the dry atmosphere of 
Arizona. 
TaBLE 15.—A comparison of stomatal measurements taken by the absolute alcohol method 
and the picric acid method. Cissus and Parkinsonia, November 17, 1912. 
Absolute alcohol. Picric acid in cedar oil. Light. 
l w Viw l w Viw 1 w Viw 
Cissus. 
Sb00M SI ccs od cated ee 71 1.4 3.1 9.1 1.4 3.5 
oa sa Dell 3.9 5.9 9.9 3.3 5.8 
9.9 3.2 5.6 9.9 2.4 5.0 
8.3 2.3 4.3 9.5 1.7 4.0 
Es | 7.6 1.1 2.9 10.6 1.1 3.2 
9.200 - PAN ieee ascancee aes 7.6 9 2.6 9.1 1.4 3.5 
Parkinsonia. 
BE OOM BM soca isce ise srlersicreyees sina 9.1 1.5 3.7 9.1 1.5 3.7 10.6 2.3 4.9 
10: 330) GUM spats, teescioyecesns ive. 0848 9.1 2.7 4.9 9.1 2.8 5.0 10.6 3.0 5.6 
12 30 am | 7.6 1.1 2.9 7.6 8 2.5 ove a aye 
2: 90: BM aewietsests aceasta | 7.6 8 2.4 6.1 9 1.5 
5.90: aeMec ores ee cgunceess -| 8.3 2.0 4.0 9.1 2.4 4.6 
After 5 hours in dark room....| 7.6 7 2.6 8.3 1.5 3.5 
After 24 hours in dark room...} Shut. 0 Shut. | Shut. 0 Shut. 
EXPERIMENTATION. 
EXPERIMENT XIV. 
During the progress of experiment V (see page 22) leaf samples for sto- 
matal measurements were taken as near the middle of each transpiration 
period as the manipulation of the experiment would permit and treated with 
picric acid in cedar oil, as described above. The values of 7'/E are repeated 
from page 23 and are plotted in fig. 20 with the values for the square roots 
of the products of the stomatal diameters. 
*Livingston, B. E., and Estabrook, A. H., Observations on the degree of stomatal 
movement in certain plants, Bull. Torr. Club, xxxrx, 15-22, 1912. 
{Browne and Escomb, Static diffusion of gases, Phil. Trans. Roy. Soc. Lond., B, 
vol. 192, pp. 270-292, 1900. 
