26 THE SMALL GRAINS 



piration for each plant, varying in accordance with dif- 

 ferent external conditions. 



28. Protection against transpiration. There are 

 various protective characters possessed by the more 

 drought-resistant plants, which serve to check transpira- 

 tion, such as a thickened epidermis, preventing cuticular 

 transpiration, and reduction of the transpiring surface, 

 by the absence or narrowness of leaves, or rolling of 

 leaves. A covering of small hairs overlapping each other 

 will obstruct transpiration. Many cereal varieties, native 

 in desert or semi-arid districts, possess one or more of these 

 protective characters. At the same time, as above 

 hinted, these varieties appear to be improved by a certain 

 amount of enforced transpiration, as they usually bear 

 more vigorous kernels and possess greater winter-hardiness 

 and resistance to attacks of fungi and insect pests than the 

 ordinary varieties of humid districts (48, 50, 53)^ The 

 same varieties also lose these qualities to a considerable 

 degree on transference to humid areas. 



