TRANSPIRATION STUDIES. 37 
three out of four cases the later maximum is higher than the first. In these 
cases, though, the relative transpiration rate again decreases before the time 
of maximum transpiration rate. In all of the four cases mentioned the soil 
moisture in the pots was probably higher than that in the ground, and since 
experiment X throws some light on the behavior of maxima in both relative 
and actual rates under different conditions of soil moisture, it is not possible 
from the potted plants to draw conclusions strictly comparable with those 
drawn from the plants in situ. 
It seemed probable that this drop and rise have some definite internal 
cause, and with the idea of obtaining some light on the cause, measurements 
were taken of the following factors: (1) stomatal openings; (2) water con- 
tent of leaves, stems, and twigs; (3) temperature of leaves. 
