LEAVES OF XEROPHYTES 



465 



The epidermis, even on the younger portions of the stem, is 

 highly cutinized, and this structure makes any evaporation 

 very slow. 



440. Leaves of xerophytes. Since the leaf is hi general the 

 main organ of transpiration, we might expect to find the leaves 

 of xerophytes highly adapted to their environment. This is the 



FIG. 359 FIG. 360 



FIG. 359. Cross section of leaf of Ficus elastica 







c, cuticle ; o, opening to pit ; p, pit leading to stoma ; s, stoma ; e, epidermal cells ; 

 w, special cells for storage of water; ch, air chamber from stoma; sp, cells 

 of spongy parenchyma ; a, intercellular air spaces. Much magnified 



FIG. 360. Fleshy leaves of Mesembryanthenmm, with stored water 

 After Giesenhagen 



case, and some of their principal means of protection from 

 excessive transpiration are as follows l : 



1. A thick epidermis, often of several layers of cells (Fig. 359). 



2. Storage of water in epidermal cells. 



3. Small stomata, often deeply sunken (Fig. 359). 



4. Epidermal hairs or scales. These are often extraordinarily 

 abundant, and in some cases give one or both surfaces of the 

 leaf a silky or silvery luster. 



1 See Warming, Lehrbuch. der (Ekologischen Pflanzengeographie, vierter 

 Abschnitt, Berlin, 1902. 



