299 



The appearance of the sand form is very different from that of 

 the prairie type, but the dift'erences are due to the edaphic xerophytic 

 conditions under which it grows. In places where this association has 

 been succeeded by trees which have induced milder xerophytic con- 

 ditions the Petalostemiim, although still growing in nearly pure sand, 

 is about normal in appearance. Figure i, Plate LI shows a plant of 

 this form in which the stems form an angle of from 5° to 15° with the 

 sand level. In some cases sand and debris have been piled up above the 

 crown, while sand beyond the protection of the stems has been blown 

 away. In such places the Petalostemiim, when growing prone, makes 

 a negative angle with the general level. In general the individual 

 plants grow apart, but on the gravel, where there is almost no ex- 

 posed sand, they grow^ so close together that the heads overlap and 

 form a tangled layer about a decimeter above the gravel level. Such 

 situations are frequent hiding-places for savanna and song spar- 

 rows. The heads of the Petalostemiim seem usually to be infested 

 with a small green caterpillar, and the leaves with tent- weaving 

 larvae. 



In the serotinal aspect, Petalostemiim continues to dominate the 

 more gravelly parts, but in other places a goldenrod {Solidago nem- 

 oralis) comes into prominence. The bright white pappus of the fruits 

 of both Andropogon scoparius and Solidago neiii oralis are character- 

 istic of the autumnal aspect. Neither of these plants loses its seeds 

 until after the sharp winter frosts. With the return of winter the 

 association assumes a dull gray color of dead leaves which resembles 

 in some particulars the arid brush-lands of the West. 



List of the Species of the Andropogon scoparius Consocies of the 

 B unch- grass A ssociation 



Dominant Species 

 Andropogon scoparius 



Secondary Species 



Arabis lyrata Aster sericcits 



Arenaria stricta Blymits cajiadciisis 



Oenothera rhombipetala Cycloloma atriplicifoliuui 



Lithospermum gmelini Hypericum kalmianum 



Petalostemiim piirpureiim f. Oenothera biennis (very few) 



arcnarium Prunus puuiila 



Solidago ncm oralis Aster miiltiflorns 



Euphorbia corollata Mosses (unidentified) 



