330 General Botany 



between 30 and 50 inches during this same period, the extent of 

 the rainfall is only from two tenths to six tenths of the evapora- 

 tion. Furthermore, in late summer this region is subject to 

 prolonged hot dry winds from the southwest. At such times the 

 temperature rises above 100° F., the humidity falls, soil moisture 

 becomes very low, and all vegetation suffers through excessive 

 transpiration. These " hot winds " were the source of great 

 losses to the early settlers when they occurred before the crops 

 were mature. On the high plains of western Kansas and eastern 

 Colorado the soil is generally dry below a depth of 6 to 15 feet. 

 The plains region is the home of occasional violent winds, tor- 

 nadoes in summer and blizzards in winter. The snowfall is 

 generally light but is subject to drifting and may become deep 

 in the depressions. 



The most characteristic grasses of the Great Plains are the 

 buffalo grass {Bulhilis and Boutelona), the bunch grass {Andro- 

 pogon), and the wire grass (Aristida). The buffalo grass is a 

 turf-forming grass, a few inches in height, which affords highly 

 nutritious forage. The bunch grasses received their name from 

 the habit of growing in scattered dense tufts, especially in lands 

 that have been disturbed by streams and wind erosion. The 

 wire grass is a coarse grass, 2 feet in height, which also grows in 

 tufts, usually mixed with other grasses. 



Just as the deciduous forests stretch westward, occupying the 

 valleys in the prairie region and the stream margins in the plains 

 country, so the tall-grass prairies extend westward in the valleys, 

 forming finger-like extensions between the tree-bordered rivers 

 and the short-grass uplands. 



At their western margin the plains are invaded on rocky slopes 

 by the western yellow pine, and at the southwest by semi-desert 

 scrub, consisting of mesquite, red cedar, and scrub oaks. The 

 grasslands also grade into sagebrush, which occupies extensive 

 areas from Colorado and Montana to the Great Basin and Sierra 

 Nevada Mountains. Scattered over the plains are many small, 



