314 



FOUNDATIONS OF BOTANY 





FIG. 220. The Duckweed, a Floating 

 Aquatic Plant. 



(Sect. 368), we must 

 consider that xero- 

 phytes 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 



1 Ficus religiosa. 



FIG. 221. Leaf of an 

 East Indian Fig Tree, 1 

 with a Slender Taper- 

 ing Point to drain off 

 Water. 



