GRIFFITHS THE GEAMA GRASSES. 347 



the highest point of the Santa Rita Mountains of Arizona. From the 

 4,500 to the 5,000 feet level on the north side of this mountain 

 B. radicosa is abundant. From about 4,500 feet down to 3,800 

 feet B. Jiliformis is commonly the prevailing species. From 3,800 

 to 3,400 feet B. rothrockii is often the most important plant, and it 

 goes here as low as or lower than any of the other perennial species. 

 Throughout this entire range, from 4,500 to about 3,500 feet, B. curti- 

 pendula may be found, but usually only upon the rougher lands, and 

 it increases in importance upward, becoming the most important 

 species upon the rocky upper foothills at 4,000 feet. Bouteloua 

 aristidoides, on the other hand, is of wide distribution and may be 

 found from the upper Bouteloua limit to the lower mesas (PL 67, 

 facing p. 343), and even across them clear to the lower Colorado and 

 into the Salton Sink below the level of the sea. Its greatest develop- 

 ment is in the lower part of the perennial grass region, about the 

 3,500 feet level. It is found, in occasional years only, where there is 

 a temporary accumulation of flood water, also in favorable places in 

 the mesas, where the regular annual accumulation commonly pro- 

 duces perennial species of Hilaria. In this general Bouteloua belt, 

 mostly at about 4,000 feet, may be found scattering patches of 

 B. parryii, B. eludens, and B. eriopoda, and, especially below, B. har- 

 bata is frequently met with. 



Roughly speaking, the great Bouteloua region of the world ex- 

 tends from Saskatchewan and Manitoba southward between the 

 Mississippi River and the Continental Divide. The western border 

 crosses the Divide in Wyoming, extends into the southern Great 

 Basin region, and strikes the Pacific coast at about the Mexican 

 boundary. In Mexico the grama grasses extend from coast to coast, 

 reaching their greatest development upon the highland, and dis- 

 appearing entirely in tropical situations of uniform heavy humidity. 

 They are especially abundant and important in those elevated 

 regions which have a heavy summer precipitation and are compara- 

 tively dry the rest of the year. Bouteloua curtipendula is common in 

 the eastern United States and B. hirsuta is prominent in portions of 

 Florida. 



The writer's knowledge of South American species is based entirely 

 upon a study of meager collections which do not warrant any con- 

 clusion other than that the species appear to be more or less com- 

 mon in the Cordillera region. A few species are of frequent occurrence 

 in portions of the West Indies and other continental islands. 



