91 



in the middle, of the variety lanceolata. Considering all lines of 

 evidence, it seems conclusive that these two varieties hnd their op- 

 timum habitat in the basins, colonize in the blowouts after the basin 

 is formed, and occupy a place similar to that of the grass Rcdfieldia 

 in the blowouts of Nebraska. The other species represented in the 

 blowouts are Lithospcnuuiii Giiicliiii, Euphorbia corollata, and Les- 

 pcdeza capitata. Each of these has deep roots, but they can not live 

 in the more active blowouts, which are either bare or with Accrates 

 alone. Rarely a few annuals, of species occurring also on the lee 

 slope, are found with Acerates, but it seems probable that their oc- 

 currence indicates at least a partial or temporaiy cessation of wind 

 erosion. If this is the case, they should be regarded as a mere ex- 

 tension of the blowsand association, in which the Acerates is per- 

 sisting as a relic. The perennial Lespedesa capitata is also good 

 evidence of the same condition, since, as will be shown later, it is 

 one of the most abundant pioneer species in the stabilization of this 

 part of a blowout. 



THE WINDWARD SLOPE ASSOCIATION 



As the erosion of the blowout proceeds, the windward slope is 

 formed, as already described. From this, sand is being removed by 

 the wind and is also settling down by gravity. There is little chance 

 for seed burial, because the same wind that carries out sand will 

 also blow' away the seeds, and as a consecjuence the annual plants 

 are absent. But the action of gravity, which brings down sand from 

 above, may also bring down plants. The principal vegetation, there- 

 fore, is composed of perennials or grasses of the Paniciiin pseudopu- 

 hescens association which are undermined and gradually slide down 

 the slope into the basin. The most frequent species is Panicum 

 pseud opnbescens itself, which seems admirably adapted to live in this 

 shifting substratum. Its usual associate, Carc.v lunhellata, also has 

 the same property. These two species seem able to live on this slope 

 under almost any condition of angle or rate of erosion. Scattered 

 bunches may be found on the steep slope below vertical walls of sand 

 capped with the same species. The wall is held vertical by the roots 

 of the grass, until finally a portion of it topples over. If the grasses 

 happen to fall right side up they continue their growth and event- 

 ually land at the foot of the hill. Many, if not all, of the remaining 

 grasses of the same association appear on the gentler windward 

 slopes, where the erosion takes place more slowly. The grasses ob- 

 served are* Lcptoloina cognatuin, Care.v Muhloihergii, Andropogon 

 scoparius, Boutcloua hirsuta, and Panicum virgatum. Lespedeca 



