142 A TEXT-BOOK OF GRASSES 



Arrhenatherum elatius bulbosum (Par. 241) may serve for storage, 

 although the plant last mentioned is not a xerophyte. 



In general, xerophytic grasses have become adapted 

 to their surroundings by the production of impervious 

 epidermis or of mechanical tissue in leaves and stems and 

 by fine foliage. Roll-leaves, described in a preceding 

 paragraph (Par. 139), are common. The foliage of xero- 

 phytic grasses is nearly always firm and hard from the 

 excessive development of sclerenchyma fibers and other 

 mechanical tissue and the relative lack of soft parenchy- 

 matous tissue. The stomata are in protected places, in 

 the longitudinal furrows of the blades or on the inside of 

 rolled blades. All these structures tend to retard evapo- 

 ration and prevent the loss of water which cannot readily 

 be obtained from the dry soil. 



There are four chief habitats where xerophytic grasses 

 may be found, — prairie, sandy soil, rocks and desert. 



179. Prairie is open grass land where the soil is deficient 

 in moisture. If open grass land occurs upon soil in which 

 there is no deficiency of moisture it may be swamp, tundra 

 or mountain meadow as indicated under a preceding 

 paragraph (Par. 177). Prairies are found as isolated 

 areas interspersed through regions that are chiefly occupied 

 by a mesophytic flora, as the eastern united States. In 

 Iowa and Missouri, they occupy large areas, with wood- 

 land interspersed. A vast prairie extending from Texas 

 northward far into Canada is called the Great Plains. 

 Similar regions in western Asia are called steppes and in 

 South America are called pampas and llanos. In Central 

 America and in some other countries, they are known as 

 savannahs (or savannas). The dominant plants of these 

 prairies and plains are grasses. In general, there are 

 many species producing rhizomes or stolons so that much 



