THE STEM AND THE LEAF 71 



clothing of dry hairs, which often assume very curious forms 

 (Fig. 57). These may completely cover one or both surfaces 

 of the leaf (usually the lower one). Such hair-clad leaves are 

 very commonly found on mountain and desert plants and on 

 those which grow in regions with a long and rainless summer, 

 and it has been experimentally proved that the hairs greatly 

 lessen evaporation from the leaves. Speaking of the flora of 

 the summer-dry Mediterranean region, the distinguished Aus- 

 trian botanist Kerner says : " The trees have foliage with gray 

 hairs ; the low undergrowth of sage and various other bushes 

 and semi-shrubs ... as well as the perennial shrubs and 

 herbs growing on sunny hills and mountain slopes, are gray 

 or white, and the preponderance of plants colored thus to 

 restrict evaporation has a noticeable influence on the charac- 

 ter of the landscape. He who has only heard from books of 

 the evergreen plants of the Greek, Spanish, and Italian floras, 

 feels at the first sight of this gray vegetation that he has been 

 in some degree deceived, and is tempted to alter the expression 

 ' evergreen ' into * ever gray.' " 



Hairs which contain liquid, like the gland-bearing one in 

 Fig. 58, do not serve to prevent evaporation, but are some- 

 times of much use for other purposes, as in carnivorous plants 

 (Chapter XXI). 



