104 BOTANICAL GAZETTE [AUGUST 
extremely high evaporation. Why there should be such a decrease 
at the 21st hour is not known. The first ratio 1.74 is approxi- 
mately equal to the normal. The day reading is 0.68. The ratio 
on August 5 is 1.54, but the 9th hour reading gives a value that is 
much lower than the usual minimum. With a slight decrease 
in the minimum, the ratio between the two becomes greater than 
before. From these data on the basis of the ratio between day and 
night foliar transpiring power values it is evident that, if the ratio 
is to be used during the process of wilting, it can only be applicable 
when the maximum is greater than the usual minimum. Through- 
out the series of both Ia and Id the ratio does not deviate very far 
from unity, but in the formation of the ratio there is an evidently 
greater corresponding decrease in the day value as compared with 
the night reading. In both cases the extent of daily fluctuation 
for the younger leaves is very small after the first day. 
The rate of evaporation throughout fluctuated considerably, 
but is unusually high for the climate of Chicago. There is neverthe- 
less no close agreement between evaporation and foliar transpiring 
power during the march of wilting. Plants similar to the ones 
used in the experiment were treated like Ia and Ib and were placed 
in a moist chamber at their respective times of wilting. They 
behaved in a similar manner and failed to recover in the allotted 
time. Although the plants were watered at the same time with 
approximately the same amount of water, figs. 5 and 6 show 
indirectly that there was much difference in the soil moisture 
content. The plant designated as Id was larger than Ia, and would 
be expected to wilt first. This observation is borne out in the 
experiment. It is also evident from an examination of the two 
graphs that the soil of Ib was drier at the beginning than that of 
Ia, as the indices of foliar transpiring power are much smaller. 
STOMATAL DIFFUSION 
The index of foliar transpiring power in its very definition is 
associated with that of vapor tension. The decrease in the index 
of foliar transpiring power such as is present at night during 
the daily march represents a great force. A solution may also 
carry with it just as great a force. Livincston (27), com- 
