70 



PRACTICAL BOTANY 



Some trees and many shrubs in countries like the Medi- 

 terranean region and California, where the hotter months are 



B C 



FIG. 57. Hairs which protect leaves from excessive loss of moisture 



A, T-shaped hairs of wormwood ; B, silky hairs of Convolvulus; C, shield-shaped 

 scaly hairs of Elseagnus. All considerably magnified. After Kerner 



nearly rainless, are summer-deciduous, losing almost or quite 

 all of their leaves at the beginning of summer. Twigs in 

 this leafless summer condi- 

 tion have been found to 

 lose only about ^ as much 

 water in a given time as 

 they do when in full leaf. 

 63. Hairs and other cover- 

 ings of the leaf surface. The 

 leaves of many kinds of 

 plants are covered with a 

 layer of wax or of a var- 

 nish-like material ; some are 



coated with a deposit of FIG. 58. Part of epidermis of geranium 



(Pelargonium), surface view 



lime salts, and all of these 

 substances appear to hin- 

 der excessive loss of water 

 from the leaves. A similar 

 purpose is subserved by a 



A, hairs, the one at the left consisting of one 

 cell, the one at the right several-celled and 

 bearing a gland at its tip ; e, stout cells of 

 the epidermis, which serve to support the 

 hair. Between the hairs a stoma is seen, 

 Considerably magnified 



