166 



( 'assia, however, can not grow upon such rapidly shifting sand 

 as Cenchrus can. and both are surpassed in this by Cycloloma 

 atriplicifolium. Cristatella Jamesii is absolutely confined to 

 blow-sand (PI. XX., Fig. 1), and disappears when the blowing- 

 is stopped. 



Numerous other species may occur, such as Croton glandu- 

 losus, Euphorbia Geyeri, Ambrosia psilostachya, Sporobolus cryp- 

 tandrus, Mollugo verticillata, and Acerates viridijiora. Others, 

 less abundant, are usually relics of the bunch-grass association, 

 the original occupant of the territory, which have persisted 

 because their sand-binding adaptations have prevented their 

 being undermined and blown away. 



Blowouts of any age may be filled up and converted into 

 level stretches of blow-sand, covered with the blow-sand asso- 

 ciation already described, but with more Cycloloma and less 

 ( 'assia in the older ones. The vegetation is always sparse, and 

 the blowing of the sand during the fall and winter is sufficient 

 to prevent the perennials of the bunch-grass association from 

 gaining a foothold. Over wide stretches of blow-sand there is 

 frequently absolutely no vegetation, while on others there is 

 nothing but Cycloloma, Ambrosia, Cassia, and Cenchrus. 



Counts in a developing blowout and in a few typical areas 

 of blow-sand are here given. 



TABLE IV. SMALL BLOWOUT. 



Cassia chamascrista 

 Ambrosia psilostachya 

 Cenchrus tribuloides 

 Cristatella Jamesii 

 Froelichia campestris 

 Euphorbia Geyeri 

 Lithospermum linearifolium 

 Oyperus Schweinitzii 

 Cycloloma atriplicifolium 

 Monarda punctata 



* See p. 156. 



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