Jan. 3,1916 
Hourly Transpiration Rate on Clear Days 
633 
The last portion of Table XXXVI gives the relative transpiration for 
different parts of the day. The percentage of the transpiration taking 
place during daylight is very uniform, ranging from 94 per cent for oats 
to 97 per cent for amaranthus and alfalfa. The transpiration during the 
night is remarkably low, ranging from 3 per cent for amaranthus and 
alfalfa to 6 per cent for oats. The data as presented represent the inte¬ 
gration of the transpiration and radiation for hourly intervals, so that the 
transpiration for the hour interval during which sunrise (or sunset) 
occurred has been included as daylight transpiration. The ratio can be 
more accurately determined from the automatic records, which show an 
Fig. 17.—Comparison of the transpiration graphs plotted in percentage of the maximum with the tem¬ 
perature graphs plotted in percentage of the maximum range. 
average night transpiration less than 5 per cent of that occurring during 
daylight. This low night transpiration is significant when we consider 
that the temperature and the saturation deficit are relatively high during 
the early hours of the night and that the dew point is seldom reached at 
Akron.^ The wind velocity at night is also at least one-half the average 
daylight velocity. 
It will be seen from Table XXXVI that the transpiration in the fore¬ 
noon is lower than in the afternoon, the difference being greatest in the 
case of rye and least in the case of wheat, oats, and alfalfa. For the 
