1918] BAKKE—WILTING gI 
were chosen, Ia, having the dimensions 5 x8 cm., and Ia., 4X6 cm.; 
from plants Id two leaves were chosen, Ib,, 7X9 cm., and Ib., 34 
cm. Whenever a new leaf became sufficiently large for the applica- 
tion of the clip, approximately 3X4 cm., it was included with the 
others. The readings were begun on the 18th hour of July 21 
and continued at hourly intervals for 24 hours. Readings were 
' taken at the same time from a standardized Livingston cylindrical 
form of atmometer. The results for plant Ia are given in table III. 
This series shows that the march of the foliar transpiring 
power is the same as has previously been pointed out (2, 4, 28, 40), 
in that the maximum transpiring power is attained at a time 
previous to the greatest evaporation. The highest index occurs 
usually at the roth and 11th hours, while the evaporation maximum 
occurs usually on the 14th hour. On account of the larger num- 
ber of readings it is to be expected that the graphical representation 
(fig. 2) will show less abruptness than has formerly been presented. 
Recalling that the leaf represented by Ia; is older than Ia,, it 
is plain that the index of foliar transpiring power is higher for the 
younger leaf almost entirely throughout the 24-hour period. The 
maximum for Ia, is at the 11th hour, when it is 0.93. This value 
is again in evidence 2 hours later. For Ia, the highest value is at 
the roth hour, when the transpiring power value is 1.00. This 
same value is again reached at the 12th hour. It is evident that 
the younger leaf Ia, reaches its maximum at an earlier period than 
the older leaf Ia,. This feature substantiates similar conclusions 
reached by BAKKE and Livincston. Another important feature 
in connection with the graph showing the march of foliar transpir- 
ing power is the sudden drop for both leaves. The lowest point 
(0.59 for Ia, and 0.67 for Ia,) occurs on the 14th hour. At the 
15th hour the index values are respectively o.91 and 0.93, while 
the corresponding values at the 13th hour are 0.93 and 0.83. 
Although the drop is the feature in the afternoon readings, the 
recovery occurring at the 15th hour is always below that of the fore- 
noon maximum. In the present case there is not much difference, 
being o .91 for Ia,; for the younger leaves there is a greater variation, 
being ©.93 at 15:00 o’clock and 1.00 for the 10:00 and 13:00 
o'clock readings. At the 14th hour the average reading for the 
