630 
Journal of Agricultural Research 
Vol. V, No. 14 
and sorghum; and later than the temperature for amaranthus. This is in 
evidence in figure 17, in which these two graphs alone are plotted for each 
plant measured. The transpiration in the afternoon always falls off far 
more rapidly than the temperature, and when the transpiration has 
reached the night level the temperature is still above the minimum by an 
amount corresponding roughly to one-third the daily range. 
The wet-bulb depression and the air-temperature curves are very 
similar in form, owing to the fact that with a uniform absplute-moisture 
content of the air the former curve is determined strictly by the latter. 
The transpiration rises in advance of the wet-bulb depression (fig. 18) in 
every instance except amaranthus, in which the graph starts later but 
crosses the wet-bulb depression curve about 9 a. m. The transpiration 
falls more rapidly than the wet-bulb depression in every instance. 
Fig. 14.—Graphs showing the hourly transpiration of Amaranthus retroflexus and the hourly values of the 
cyclic environmental factors, aU plotted in percentage of the maximum or maximum range. 
The evaporation rises later than the transpiration graph (fig. 19) in 
the case of alfalfa and amaranthus, owing to the fact that the tank 
evaporation is determined largely by the vertical component of the radia¬ 
tion, while isolated pots of plants probably receive radiation in excess 
of the vertical component. In the case of rye, the two graphs coincide 
during the early morning hours, but a marked depression of the trans¬ 
piration curve from the evaporation graph occurs at 8 a. m., this differ¬ 
ence persisting until after the evaporation graph has passed its maxi¬ 
mum. The comparison of the two graphs brings out very strikingly the 
depression in the transpiration graph of rye during the morning hours, 
to which attention has already been called and which is a common 
feature of the cereals so far investigated. 
The evaporation graph in the early afternoon falls in advance of the 
transpiration graphs, but owing to the greater slope of the transpiration 
