Jau. 3,1916 
Hourly Transpiration Rate on Clear Days 
597 
The smoothness of the graphs obtained by this method of composites 
is in evidence in figure 4. The radiation curve is again seen to be sym¬ 
metrical with reference to the noon hour and to decrease in either direc¬ 
tion, at first slowly and then rapidly, to zero, a type of curve character¬ 
istic of clear days. The air temperature, wet-bulb depression, and 
transpiration all reach their maximum about two hours later. The 
transpiration graph for oats, like that for wheat, gives evidence of a slight 
depression or undue flattening after 9 a. m. In other words, one would 
expect from the corresponding slopes of the radiation and temperature 
curves that the transpiration graph would be more convex through the 
period from 9 a. m. to 2 p. m., provided the oat plant responds as a free 
physical system. It will be noted that the transpiration rate also falls 
off more rapidly in the afternoon than does the air temperature or the 
wet-bulb depression. In this respect the transpiration graph corresponds 
rather strikingly with the solar-radiation and wind-velocity graphs. The 
increase in wind velocity during the night does not, however, produce 
a corresponding increase in transpiration. This point will be referred 
to again. Finally, it is of interest to note that the transpiration loss of 
oats under Akron conditions during the night hours is extremely small, 
compared with the loss during the day. 
SORGHUM 
The sorghum transpiration measurements, like those made with 
wheat and oats, were conducted inside the screened inclosure and include 
three varieties of Andropogon sorghum —namely, Minnesota Amber, milo, 
and Dwarf milo 1 (Table X). 
The environmental measurements for the corresponding period are 
given in Tables XI to XIV, inclusive. 
1 Minnesota Amber, A. D. 1 .341-13; milo, S. P. I. No. 34960: Dwarf milo, S. P. I. No. 24970. 
