150 PASTORAL AND AGRICULTURAL BOTANY 



do many lichens and mosses, and to revive quickly when water is again 

 supplied. During periods of excessive precipitation, both species of 

 grasses grow and fruit luxuriantly. These short grasses have a very 

 extensive surface-root system and are especially adapted to conditions 

 found in the Great Plains region. After a slight rain, when only the first 

 few inches of the soil becomes wet, these plants are able to absorb water 

 and grow. Ordinarily grazing does not modify appreciably the short- 

 grass cover. It seems to favor the development of the short -grass. 

 Grass fires, if repeated, kill out the buffalo grass, but apparently grama 

 grass suffers little. Extensive grazing causes the reversion of the short- 

 grass stage to an earlier stage in the succession where Gutierrezia sarothrce. 

 and Attmisia frigida become dominant. 



The presence of a short-grass cover indicates a growing season that is 

 shortened by the limitation of the water supply. Crops which mature 

 early are, therefore, more likely to succeed on this type of land than crops 

 which require a longer season, such land is not adapted at all to deep- 

 rooted crops unless the plants are grown far apart. 



The above descriptions of a number of important agricultural grasses 

 does not exhaust the list of native and introduced grasses, which in vari- 

 ous parts of our wide domain figure largely in the composition of the vegeta- 

 tion of the inclosed meadows of the eastern states and the open wild 

 ranges of the western states. A detailed account of all these grasses and 

 their life histories would fill a large volume. 



BIBLIOGRAPHY 



BALL, CARLETON R.: Johnson Grass. Bulletin n, Bureau of Plant Industry, U. S. 



Department of Agriculture, 1902. 

 BALL, CARLETON R.: Saccharine Sorghums for Forage. Farmers' Bulletin 246, U. S. 



Department of Agriculture, 1906. 

 BENTLEY, H. L.: Experiments in Range Improvement in Central Texas. Bulletin 13, 



Bureau of Plant Industry, U. S. Department of Agriculture, 1902. 

 BROWN, EDGAR and HILLMAN, F. H.: The Seeds of the Blue Grasses. Bulletin 84, 



Bureau of Plant Industry, 1905. 

 CARRIER, LYMAN: Cost of Filling Silos. Farmers' Bulletin 292, U. S. Department of 



Agriculture, 1907; The Grazing Industry of the Bluegrass Region. Bulletin 397, 



U. S. Department of Agriculture, 1916. 

 GATES, J. S. and SPILLMAN, W. J.: A Method of Eradicating Johnson Grass. Farmers' 



Bulletin 279, U. S. Department of Agriculture, 1907. 

 CLEMENTS, FREDERIC E.: Plant Indicators. The Relation of Plant Communities to 



