34 fl> o s t e i s i a 



Together with the lower foothills the 

 mesas form the battle ground where is 

 waged the war between the highland 

 and the lowland plants. At one sea- 

 son of the year the vegetation of the 

 mesas has the character of the moun- 

 tain region. At another season the 

 prairie plants are more abundant. The 

 changes may take place with almost 

 kaleidoscopic speed. The slight 

 change in the angle of the sun's 

 ays replaces the white flowered prairie 

 sand lily (Leucocrinum) with the blue 

 Pentstemon or larkspur of higher alti- 

 tudes. Later the prairie Yucca comes 

 into blossom, and then there appear 

 great yellow masses of Arnica, the near 

 relatives of which belong to the higher 

 altitudes. Then come again prairie 

 plants, the wall flower Erysimum and 

 the yellow puccoon {Lithospermum). 

 Soon appear the white and purple 



