206 



ELEMENTARY STUDIES IN BOTANY 



the epidermis is always present, but the amount of cuticle 

 (Fig. 158) may vary widely. It is in plants of dry regions 



that the cuticle may 

 become very thick, 

 layer after layer being 

 added to it by the 

 epidermal walls be- 

 neath. In some cases 



the cut j c l e 



SO thick that the 



, , . 



SRgewayS through it to 



the stomata resemble 



short tubes (Fig. 168), the stomata being said to be " sunken." 

 The layer of palisade cells (Fig. 157), which is developed 



FIG 170. - Section through the leaf of bush clover, 

 showing the usual leal structure, and also the 

 numerous simple hairs produced by the lower 

 epidermis ; observe that the hairs bend sharply 

 and lie along the surface of the leaf. 



FIG. 171. Branching hair of FIG. 172. Scale from the leaf of Shepardia ; such 

 mullein. scales overlap and form a complete covering. 



in leaves whose two surfaces are unequally illuminated, 

 must tend to diminish transpiration by exposing only the 



