94 | BOTANICAL GAZETTE [AUGUST 
absorption and incipient drying, an additional force must be 
present in order to cause the water to be pulled into the cells to a 
greater degree than before. If this interpretation is correct, the 
older leaves (on account of their closer proximity to the absorption 
center) should show a more complete revival. This speculation 
would necessarily be based upon the readings of the secondary 
maxima. The comparative values become evident, for Ia has a 
maximum of 0.93, falls to 0.59, and subsequently returns to 0.91; 
for Ia, the maximum is 1.00 and comes back from 0.97 to 0.86. 
This fall and subsequent rise are independent of the evaporation 
rate. 
The march of the foliar transpiring power is more or less definite. 
This is especially true as it bears upon maximum and minimum 
values. For Ia the maximum value occurs on the 11th hour with 
an index of 0.95, while the minimum value 0.50 is on the 23d hour. 
The ratio between maximum and minimum is 1.9. For Ia, the 
maximum value, 1.00, is in evidence on the roth hour, while the 
reading 0.58 on the 2d hour of July 22 gives the minimum value. 
The ratio in the latter case is 1.72. : 
Another important feature presented by the present series is 
the high value on the 17th hour of July 22. In the previous 
experiments which have dealt with foliar transpiring power, there 
has been a fall in the transpiring power value after the secondary 
rise. It is noticed that the evaporation during the afternoon is 
rather intense, being 1.6. The high value of the transpiring power, 
therefore, is without question due to the high evaporating power 
of the air. 
In formulating a graph (fig. 3) from the data presented in the 
march of foliar transpiring power, the general feature is the high 
foliar transpiring power before the time of greatest diurnal evapo- 
ration. For both leaves the maximum is reached at the 11th hour, 
when the index is 1.00. This value is retained for Id, until the r2th 
hour, and for Id, until the 13th hour. The minimum value (0.47) 
for Ib, occurs on the 22d hour, while for Ib, (0.44) it occurs on the 
18th hour. The ratio of maximum to minimum or of day value 
to night value is 2.1 for Ib, and 2.3 for Ib,. The sudden drop in 
the afternoon reading on the r4th hour is equally as striking as that 
