766 



TEXTBOOK OF BOTANY 



a great variety of flowering herbs, notably legumes and composites, add 

 color to the landscape when in bloom. Just as the tall grass prairie was 

 invaded by deciduous associations along the stream courses, the mixed 

 prairie was invaded along river bottoms and terraces by finger-like ex- 

 tensions of the tall grasses. Trees are more restricted to stream margins, 

 seepage areas, and ravines. 



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tvM 





M^J'M 



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Fig. 391. A dense sod prairie of needle grass {Stipa spartea) and slender wheat 

 grass {Agropyron tenerum) in the central northern grasslands. Photo by H. L. 

 Shantz. 



In the mixed prairie the several divisions of crop plants mentioned 

 under the tall grass prairie reach their western limits. Beginning in the 

 south and going northward one passes by fields of cotton, kaffir com and 

 milo, hard winter wheats, corn and alfalfa, and finally hard spring wheat 

 and hay in Canada. 



The western high plains are characterized by short grasses, especially 

 grama and buffalo grass, with local areas of taller species common to the 

 mixed prairies. This is a region of restricted rainfall and only the upper 

 two or three feet of soil contains water. Here water evaporates both at 

 the upper soil surface and at the under surface of the moist horizon. 



