70 



PRACTICAL BOTANY 



Some trees and many shrubs in countries like the Medi- 

 terranean region and California, where the hotter months are 



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



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

 scaly hairs of Elxagnus. All considerahly 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 witli a 

 layer of wax or of a var- 

 nish-like material ; some arc 

 coated witli a deposit of 

 lime salts, and all of these 

 substances appear to hin- 

 der excessive loss of water 

 from the leaves. A similar 

 purpose is suliserved by a 



Fig. 68. I'art of epidermis of geraiiimii 

 {Pelargonhnn), surface view 



/i, hairs, the one at the left consisting of one 

 cell, the one at the right several-celled and 

 hearing a gland at its tip ; .», stont cells of 

 the epidermis, which serve to support the 

 hair. Between the hairs a stoma is seen. 

 Considerahly magnified 



