INFLUENCE OF WATER ON LAND-PLANTS 45 



thorns ; in less xerophytic situations the thorns are 



absent. 



Certain pecuHarities 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 hght 

 as possible, and the 

 leaves are so arranged. 



Fig. 14. — Cytisus scoparius (Common 

 Bkoom). (Slightly Magnified.) 



1. Transverse section of green assimi- 

 lating stem. o, Bolerenohyma ; 

 6, 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 

 (o), epidermis (6), and ohlorophyll- 

 tissue (c). 



Fig. 15. — Ruscus acvleatus 

 (Butchek's-Bkoom), showing 

 Cladodbs arising in Axils 

 OF Leaves and Each bearing 

 A FlowBe. (Natubal Size. 

 Ajfter Kbrner.) 



with respect to each 

 other, that every avail- 

 able portion of space 

 upon which light falls is 

 occupiied 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 



