INFLUENCE OF WATEE ON LAND-PLANTS 45 



thorns ; in less xerophytic situations the thorns are 



absent. 



Certain peculiarities in the arrangement and display 



of the leaves are also to be recognized as xerophytic 



^ _~ adaptations. The hygro- 



phytic type of leaf 

 spreads out its surface 

 to catch as much light 

 as possible, and the 

 leaves are so arranged, 



FIG. 14. Cytisus scoparius (COMMON 

 BROOM). (SLIGHTLY MAGNIFIED.) 



1. Transverse section of green assimi- 

 lating stem. a, sclerenchyma ; 

 b, chlorophyll - tissue ; c, cortex ; 

 d, phloem ; e, cambium ; /, xylem ; 

 g, pith ; h, epidermis possessing 

 stomata at intervals. 



2. Portion of outer tissues, magnified 

 more highly to show thick cuticle 

 (a), epidermis (6), and chlorophyll- 

 tissue (c). 



FIG. 15. Ruscus aculeatus 

 (BUTCHER'S-BROOM), SHOWING 

 CLADODES ARISING IN AXILS 

 OF LEAVES AND EACH BEARING 

 A FLOWER. (NATURAL SIZE. 



. AFTER KERNER.) 



with respect to each 

 other, that every avail- 

 able portion of space 

 upon which light falls is 

 occupied by a leaf (see 



leaf -mosaic, p. 68). The leaves of xerophytes, on the 



other hand, are not displayed in this way. 

 Direct sunlight promotes transpiration, and as this is 



