GRIFFITHS—THE GRAMA 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. filiformis is commonly the prevailing species. From 3,800 
to 3,400 feet B. rothrockia 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 
aristidovdes, on the other hand, is of wide distribution and may be 
found from the upper Bouteloua limit to the lower mesas (PI. 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. parry, B. eludens, and B. eriopoda, and, especially below, B. bar- 
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. Boutelowa 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. 
