642 



ZONES AND REGIONS [Pt. Ill, Sect. II 



of Piptocalyx circumscissus, 7 mm. ; and of 



caroliniana micrantha, 16 mm 

 Stylocline micropoides, 9 mm. 



Just as in the Sahara, the ephemeral rain-plants of the North American 

 desert do not exhibit any marked xerophilous structure. 



The desert-like character of certain tracts of country at the eastern base 

 of the Sierra Nevada, due to the combined action of soil and climate, 

 attains its maximum in the ' Bad Lands' (Figs. 378, 381, 384) lying between 



Fig. 380. North American desert-flora. Tetradymia canescens, DC. i. One-third natural 

 size; 2. magnified 2. From a specimen in the Berlin Herbarium. 



the Platte and Missouri rivers. This district possesses the scantiest vegeta- 

 tion, is richly creviced and broken up, and its loose soil, deeply furrowed 

 by each fall of rain, constantly changes the form of its surface (Figs. 378, 

 381). There is frequently not a trace of vegetation over wide stretches of 

 country. Thus Rydberg states : ' Here was a tract of land several sections 1 

 in area consisting of canons, following one another in succession, and 

 separated by narrow ridges. Not a speck of green was visible.' 



Two chenopodiaceous plants form the main mass of the meagre vegeta- 

 tion, Sarcobatus vermiculatus, a thorny, succulent shrub, a half to one meter 

 in height (Fig. 383, 2, 3), and the white woolly Eurotia lanata (Fig. 383, 7). 



1 A section = 1 sq. mile = 2-59 sq. km. 



