314 



FOUNDATIONS OF BOTANY 



FIG. 220. The Duckweed, a Floating 

 Aquatic Plant. 



(Sect. 368), we must 



^JSP^^ZTIZV consider that xero 



S_~dSi^ pyhtes are highly spe- 



cialized and modified 

 forms adapted to ex- 

 tremely trying condi- 

 tions of life. A typical 

 xerophyte is one which 

 can live in a very dry 

 soil in a nearly rain- 

 less region. The yucca 

 in Plate VII and the 

 melon-cactus (Fig. 49) 



are good examples of such plants. 



Less extremely xerophytic are plants 



like the date-palm (Fig. 54), which 



flourishes in the oases of the Sahara, 



where the soil is moist from the 



presence of springs, though rains are 



almost unknown, or the houseleeks 



and stonecrops found in many gar- 

 dens, the so-called Spanish moss 



(Plate IV), and lichens (Figs. 198, 



199), all of which grow most rapidly 



in moist air, but cling to bare rocks 



and trunks of trees, from which they 



get no water. A xerophyte must 



be capable of storing water and tran- 



spiring very slowly, like cactuses, 



aloes, Stonecrops, and SUCh fleshy plants with a Slender Taper- 



ing Point to drain off 

 1 Ficus religiosa. Water. 



