546 BOTANY 



true prairie region is reached. Here no trees can grow except in the 

 shelter of ravines or along the beds of streams, where Cottonwoods 

 and Willows are generally found, even in the arid western part of 

 the prairie region. The typical prairie consists of various grasses 

 (e.g. Andropogon, Chrysopogon), which form a continuous turf in the 

 moister eastern prairies, but in the dry western plains are scattered 

 in tufts over the bare soil. Of these bunch grasses one of the most 

 characteristic is the Buffalo-grass (Bulbilis dactyloides). 



The eastern prairies are gay in early summer with many beautiful 

 flowers Phlox, Dodecatheon, Violets, Verbena, Castilleia, Lithosper- 

 mum ; and later appear the showy Compositae, Silphium, Rudbeckia, 

 Erigeron, Solidago, Aster, Coreopsis, Gaillardia, etc. Further west- 

 ward, where the ground has been broken up, Sunflowers (Helianthus 

 annuus) appear in countless legions. 



Western Kansas, and Nebraska, and eastern Colorado are occupied 

 by arid plains with sparse vegetation, and approach in the character 

 of their vegetation the deserts of the far West. Yucca, various low 

 Cacti, and Sage-brush (Artemisia) suggest the strictly xerophytic 

 growths of the true deserts. 



The great differences in the flora of the same latitude due to 

 the topography are most strikingly seen in the journey from New 

 Orleans to Los Angeles in Southern California. The Gulf region 

 of Louisiana, with its swampy forests, presents an almost tropical 

 luxuriance of vegetation. Passing westward across Texas, the dense 

 forests of the coast soon give way to scattered groves of Pines, evidenc- 

 ing the marked falling off in the rainfall, which becomes still more 

 pronounced in the western part of the state, where there is a prairie 

 formation with only a scattered growth of stunted trees, principally 

 the Mesquit (Prosopis). In the early summer these prairies show 

 many beautiful flowers, several of which are garden favorites, such 

 as the common Drummond's Phlox, Gaillardia, (Enothera, etc. 



Deserts. Journeying westward, another factor in determining the 

 vegetation is encountered, the southern extension of the Rocky 

 Mountains. On the westward side of the divide, in New Mexico 

 and Arizona, the region is a true desert with a very scant vegeta- 

 tion, including a number of most characteristic American types. Of 

 these the first in importance are the Cacti, which reach their greatest 

 development here and in the neighboring Mexican highlands. The 

 strange forms of the giant Cactus (Cereus giganteus), once seen, are 

 never to be forgotten. In June, many of the Cacti are covered with 

 their showy crimson and yellow flowers, and with the magnificent 

 flower-clusters of the Yuccas, make a very striking floral display. 

 The Century-plant and other Agaves also occur in this region, but 

 are more abundant farther south. 



Entering California, we cross the desolate Mojave desert, absolutely 



