not obviously great, the foliage of the ocotillo and of Verbena will continue 

 normal for a fairly extended period. When the soil- water is sufficient there 

 is no evidence in the behavior of the stomata that even the highest tempera- 

 tures and strongest insolation affect the plants unfavorably. As I shall show, 

 when the conditions are so trying as to bring about wilting, the stomata then 

 close; otherwise they open to their full extent during certain portions of 

 the day, maximum dimensions having been observed day after day during 

 the hottest weather. And, moreover, as will appear, the differences of tem- 

 peratures are not without relation to the physiological processes evident 

 within the guard-cells, although these are not in the direction of reducing the 

 transpiration rate when, aside from the condition of wilting, the danger from 

 transpiration would appear to be greatest. 



