THE GREAT AMERICAN DESERT 



223 



be reduced two inches or more, but seldom are the plants uprooted. It 

 is to the rhizome habit of propagation that Redfieldia owes its success 

 in thus so completel}^ capturing the blow-out. The later invaders are 

 also provided with this device, which certainly is the key to the whole 

 situation. 



After Redfieldia has once taken charge of the habitat other species 

 soon begin to wander over the rim of the blow-out and to invade the 

 area occupied by the first blow-out pioneer. Among the first of these 

 early invaders we must number the spiny blow-out grass (Muhlen- 

 lergia pungens), sand grass {Calamovilfa longifolia), and the hair-like 

 eragrostis {EragrosUs trichodes) . From the appearance of these grasses 

 the decline of the blow-out is rather rapid. As these various species 

 wander up the steep sides, and the force of the wind striking upon 

 the upper slopes is reduced and the sand held from blowing, other 

 species wander in from the bunch-grass association. If these new 

 plants are properly provided with a rhizome device like that of their 

 predecessors they soon begin to weave themselves into the now con- 

 spicuous blow-out association. The plants that most commonly gain 

 entrance soon after the grasses have become well established are prairie 

 pink {Lygodesmia juncea), small-flowered psoralea (Psoralea mi- 

 crmitka), long-leaved milk vetch (Phaca longifolia), and the hairy 

 golden aster {Chrysopsis villosa). Indeed, some of these species may 

 get a start in the declining blow-out almost as soon as Redfieldia. 



In this manner the efi'ect of blow-out conditions are finally so far 

 removed that the bunch-grasses enter and take possession of the area 

 so well prepared by the pioneers in the succession. It is almost pa- 

 thetic to find that Redfieldia, the first plant to appear in the blow-out 



Pig. 10. A Square Meteh Quadrat in the Blow-out shown in Fig. 9. The bunch- 

 grass is now conspicuous with a few tufts of Redfieldia at the right. 



