26 
entrance and exit and by the neighboring, comparatively heavy parts of 
the wall. Anticlinal walls never strike the guard cells midway. A more 
detailed explanation of the mechanism of these stomata would be super- 
fluous here. However, there are some interesting features about their 
turgor and their behavior under changes of illumination and with the 
gradual withdrawal of their water which render it worth while to intro- 
duce some measurements. The-agent employed by me to withdraw the 
water was potassium nitrate. The solutions were 0.3 normal, 0.5 normal, 
and normal. Measurements are in microns: 
| ae: 
| 
In pure 0.8 nor- | 0.5 nor- Lnor- | 
| 
| 
water. mal. mal. mal. 
Stoma: 
| Length ._.....--------- | 34, 35 35 | 34 | 
WE Sica couse | 31 30 2 | 6 | 
| Pore, width __.-_---------- | 5 3 1.5| 0 
| Ridge of exit .-___---.------ | 9|/ . 7.5 7 | 6.5 | 
The normal solution plasmolysed the guard cells and caused the contents of 
other epidermal cells to collapse until they occupied hardly half the previously 
visible area. Remaining ten minutes in this solution killed many of the former, 
and others opened the pore only after the solution was replaced by water and the 
slide exposed to the direct sunlight. The two stomata described below half 
opened in water and completely in the sunlight. Measurements are in microns: 
| | 
| | | Obscure light. Microscope stage. 
| } . 
| Leaf. | —— 
arse 1 min- 75 min- | 10min- | 15 min- | 
| utes, utes, utes. | utes. | 
A | Width: | | 
LN aS a aS ee 32 31 29 80.5 31 
POG ctr as 5 4 3 3 4 
B | Width: | | 
BiOWA tease ant 30.5 30 30 30,5 31 
It appears from these measurements that seventy-five minutes in quite 
diffuse light affects the degree of opening of the pore about as much as 
does immersion in 0.5 normal potassium nitrate solution. ‘The recovery 
of turgescence with better illumination occurs with amazing promptness 
when one considers the great change in turgor which precedes and causes 
it. In this experiment, as is always necessary when stomata are under 
prolonged microscopic study undertaken with sufficient care to permit of 
accurate measurements, they are immersed in water. When they are in 
the natural condition on the living plant they respond much more quickly 
and thoroughly to the withdrawal of the light, as is shown by experiments 
to be reported below, in which the rapidity of transpiration is determined 
by the cobalt test. 
