84 BOTANICAL GAZETTE [AUGUST 
for lighting was replaced by electric light. The cobalt paper 
squares were warmed upon a granite pie-plate, which was adjusted 
by a clamp over an alcohol flame, so that the paper squares were 
heated to a temperature sufficient to give them the blue color. 
EXPERIMENTATION 
The readings for the 1915 series, begun on August 16, were 
usually made between the roth and 11th hours and again between 
the zoth and 21st hours. Two plants were used for the foliar tran- 
spiring power tests; two additional plants were used for the wilting 
determinations according to the method of Briccs and SHANTZ. 
Evaporation was determined at the same time by a standardized 
Livingston form of cylindrical atmometer.. The readings as 
recorded in table I show the maximum foliar transpiring power 
as occurring about the 11th hour, while the minimum usually occurs 
after sunset. Wherever possible, leaves of different ages were 
used and were numbered and tagged Ia,, Ia2, Ia;, Ib:, 1., etc., the 
highest number representing the youngest leaf. In this way the 
same leaf could be used throughout. 
The average results of the foliar transpiring power indices, 
as represented graphically (fig. 1), show a general decline from 
August 16 to August 20. The maximum index reached on Au- 
gust 17 possesses a value of 0.89. This index is almost the 
same as the one obtained earlier by BAKKE and LIVINGSTON. 
Although the plants were watered a little on the day the experi- 
ment was begun, they must have given off considerable water 
during the previous 3-day interval. That the soil moisture con- 
tent has an appreciable effect upon foliar transpiring power has 
been proven previously, and from the nature of transpiration it is 
self-evident. The Helianthus plants of BAKKE and LIVINGSTON 
were growing in a place where the soil moisture was less than would 
be regarded as optimum. In all probability the two sets of Helian- 
thus plants were grown in soil having practically the same amount 
of moisture. The soil moisture content in both series was below 
the amount necessary for the production of the greatest growth. 
For the first half of the series the highest transpiring power 
occurs during the day, while the lowest transpiring power values 
