i6 



THE PHYSIOLOGY OF STOMATA. 



the soil- water is depleted (Livingston, 1906), though sufficient may be retained 

 to carry some forms of vegetation through to the summer rainy period. 

 Verbena ciliata is in this respect remarkably hardy and, from its anatomical 

 character, quite unexpectedly so. The height of the dry season is one which 

 is trying in the extreme, one would think, and still, with a supply of water 



TABLE 8. Rainfall, Tumamoc Hill, Tucson, Arizona, for 1905, in inches. 



[See fig. 6.] 



TABLE 9. Temperatures for the year 1906, Tumamoc Hill (F.). 



