126 F. E. Clements 



Elymus sitanion, and Koeleria cristata. Even more eloquent are 

 Bouteloua gracilis and racemosa in the neighboring mountains, 

 and the unique reUct east of San Diego at Jamacha, containing 

 B. hirsuta, radicosa, and rothroc\i. On the plateau that forms the 

 eastern rim of the desert at Kingman, the desert plains consist 

 of Bouteloua eriopoda, B. gracilis, Aristida divaricata, A. pur- 

 purea, Sporobolus cryptandrus, S. c. flexuosus, S. strictus, Hilaria 

 mutica, and Muhlenbergia porteri. Still higher and to the east, 

 at Seligman, where there is a rainfall of 15 inches, most of the 

 species of the desert plains have yielded to the mixed prairie, 

 comprising B. gracilis and racemosa, Stipa pennata and comata, 

 Sporobolus, Hilaria jamesi, and others, w^ith Andropogon scopa- 

 rius, furcatus and, more rarely, nutans and halli in postclimax 

 areas, such as valleys and sandhills. 



Of the 25 species mentioned above, all but seven are transads 

 and most, if not all, of those seven must have extended some dis- 

 tance into the region concerned. The consequence was a mixed 

 prairie surpassing that of the present in wealth of species and in 

 nutritive value as attested by eight short-grasses (six species of 

 Bouteloua, Hilaria cenchroides, and probably Buchloe dacty- 

 loides) as well as by H. jamesi, which is outranked only by B. 

 gracilis and Buchloe in food value. Naturally, not all the domi- 

 nants grew intermingled, but the cover exhibited various group- 

 ings in accordance with the requirements of the species and the 

 diversity of terrain. In the wet phases of the major climatic cycles, 

 the animals must have reached not only the maximum in num- 

 bers, but also in size, as exemplified by the horses, camels, and 

 elephants of the late Pliocene and early Pleistocene. 



Among the grass transads are several tall-grasses such as 

 Andropogon saccharoides, A. glomeratus, and Imperata hoo\' 

 eri that are subtropical in nature and derivation. A larger num- 



