TRANSPIRATION UNDER CONTROLLED CONDITIONS. 61 
the box was turned as the day advanced, so that no shadow ever fell on 
plant or atmometer. The rapid evaporation caused an unavoidable lower- 
ing of temperature within the box. The polymeter had to be so placed that 
the humidity readings are probably a little too low. 
o a Base for T & E Apr. 11 
_—t 
Base for T & E Apr. 4 
7 8 9 10 ol 12 1 2 3 4 5 6 
Tia. 27.—Graphs for transpiration of plant No. 7, under 
two conditions of evaporation rate. Exp. XXII. 
These results also appear in table 24. They show that the evaporation 
conditions for No. 6 were greatly reduced and that the actual transpiration 
was greatly cut down. The maxima for both relative and actual transpira- 
tion are coincident with the evaporation maximum. Thus, without doubt, 
the drop and rise do not occur under the conditions of lessened evaporation, 
but dooccur in this same plant under more strenuous evaporation conditions. 
In the case of No. 7, the evaporation conditions were more severe than 
on April 4, but the difference is by no means so marked as was the case with 
No. 6. The actual transpiration amounts are higher than before, showing 
that the plant was capable of giving off more water than on April 4, but the 
relative transpiration is on the whole lower. Furthermore, a flattening of 
the curve of actual transpiration occurs between 11 and 1 o’clock, and the 
relative curve shows a corresponding dip and rise. Evidently the limit of 
