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E E. Clements 



western part of the Mohave, Poa scabrella, Oryzopsis, Stipa spe- 

 ciosa, Elymus sitanion, and E. cinereus grow together, and in 

 sandy areas at GoflFs and across the Colorado River at Yucca, 

 Hilaria rigid a, Aristida p-wrighti, Muhlenbergia porteri, and 

 Sporoboltis c-flexHosus occur. As would be expected, almost all 

 these are southern in origin; they belong to the grass associations 

 that border the desert today and have most recently withdrawn 

 from it. By contrast, such major dominants of the mixed prairie 

 as the two Boutelouas and Hilaria jatnesi persist only in the 

 mountains, while the boreal Stipa cofnata and Agropyrum 

 smithi have moved well to the north. 



The presence of two or more dominants from each of four 

 associations out of the six that form the prairie climax denotes 

 that the original grassland of the desert area belonged to a biome 

 much less differentiated than at present. Most wide-ranging of 

 the species concerned are Bonteloua racemosa and Sporobolus 

 cryptandrtis, which extend from the Atlantic to California and 

 from Canada into Mexico; B. gracilis and hirsuta, with a similar 

 extension from the Middle West; and Andropogon glo7neratus, 

 which stretches in a broken line from ocean to ocean in the 

 south.* 



Transads 



These are dominants or subdominants that still exist on both 

 sides of the desert and consequently must have extended through 



* Note: A steady effort has been made to verify and extend recorded ranges 

 both in field and herbarium during the past decade or more, but it is not to be 

 hoped that final accuracy can be attained in this respect. Some early records by 

 competent botanists are no longer verifiable, especially where disturbance has 

 obliterated rare extralimital stations as it seems to have done with Btichloe in 

 Canada and Arizona. For the Southwest in particular, ranges have been drawn 

 chiefly from Jepson's Manual for California, Tidestrom's Flora of Utah and 

 Nevada, and Shreve's MS catalogue for Arizona. Sargent's Manual and Sud- 

 worth's bulletins have been utilized for the drawing of tree ranges. 



