Oct. 23 ,1916 Daily Transpiration during Normal Growth Period 
167 
While large daily fluctuations occur in all the physical factors, the 
graphs do not show a marked “run” as the season advances. In other 
words, the seasonal change is not large. The evaporation shows a slight 
maximum in early August. The radiation is at its maximum in the 
latter part of June, at which time the sun reaches its greatest altitude. 
From this time onward the maximum intensity of the radiation (repre¬ 
senting cloudless days) gradually decreases. The wind velocity, on the 
other hand, tends to increase slowly as the season advances. The maxi¬ 
mum temperature and maximum wet-bulb depression occur during the 
middle of August. 
MEASUREMENTS IN 1915 
The daily transpiration measurements in 1915 were begun as soon as 
the crops were established and include, therefore, the whole growth 
period (Table III). The season was exceptionally rainy, which was 
unfortunate from the standpoint of the transpiration measurements, as 
the plants were often so wet in the morning that it was impossible to 
determine the transpiration of the preceding day. In such cases the 
mean transpiration has been given for the two or three days included in 
the rainy period. Such breaks in the daily record are indicated by 
dotted lines in figure 3, in which the data in Table III are presented 
graphically. Supplementary data relative to the plants used in the 1915 
measurements are given in Table IV. 
