






is FLOWERING PLANTS 
epidermal cells, which are large and very thin-walled, and 
when full of sap are distended; but as they lose water by 
-transpiration they contract, and thus draw together the halves 
of the blade, causing the upper surfaces to become infolded. 
The stomata are mostly on the upper surface and are situated 
in grooves, so that the leaf is thus protected from too rapid 
transpiration ; the lower surface, which alone is exposed, is 

Fig. 42.—LEAF OF XEROPHYTIC GRASS, TRANSVERSE SECTION OF BLADE. 
(Low power. ) 
é, upper epidermis ; s, position of stomata ; sed, sclerenchyma ; 1, fibro- 
vascular bundles. ~ 
protected from drought by bands of sclerenchyma beneath 
the epidermis. All these characteristic structures—the thick 
cuticle, the deep-seated stomata, the infolding of the. upper 
surface on which the stomata are, the presence of scleren- 
chyma—are protections against too rapid transpiration. 
There is yet another provision against drought: some succu- 
lent leaves, such as those of Aloe, have a layer of cells between 
the epidermis and the palisade parenchyma, without chloro- 
phyll, and containing instead much watery sap. This “aqueous 

