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 l)oth 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. 



