148 



GENERAL BOTANY 



plain regions inhabited and cultivated by man (Fig. 70). These 

 so-called mesophytes thus furnish the principal plant environ- 

 ment of the civilized races of mankind, from which have been 

 derived the main food, forage, and fuel plants which minister to 

 man's comfort and progress. The form, structure, and physiol- 

 ogy characteristic of the typical mesophytes have been sufficiently 

 outlined in the preceding account of the structure and function 

 of the root, stem, and leaf, and need not be elaborated here. 



FIG. 71. Xerophytic vegetation 



Desert vegetation made up principally of " ornamental cacti." Photograph 

 furnished by the United States Department of Agriculture 



Xerophytes. The traveler in desert regions of the United 

 States, or in sandy areas like the peninsula of Florida, is at once 

 impressed with the unusual forms assumed by the characteristic 

 native plants of these regions. In the desert conspicuous forms 

 of plant life are mostly of the contracted, cactuslike type, which 

 is in strong contrast to the expanded, broad-leaved types which 

 clothe the more productive mesophytic areas inhabited by man. 

 Plants of this type are called xerophytes (Fig 71). The reason 

 for the difference is obvious if we consider for a moment the 

 statement made at the outset of this topic, namely, that the 

 water "supply available to the plant is dependent upon the avail- 

 able soil water and upon the conditions controlling evaporation 

 in any given plant habitat. In the American deserts during the 



