88] VEGETATION REGIONS OF THE PRAIRIE PROVINCE 391 
which they are named. The bunch grass formation exhibits two 
types, the blue-stem formation, which reaches its chief develop- 
ment inthe sand hills proper, and the beard grass formation, 
which is characteristic of sandy plains and sub-sand hills. Both 
are open formations of a pronounced type ; in the first, the indi- 
viduals are 1-3 meters apart. Owing to the xerophytic nature 
ofthese formations, not only are the grasses bunched, but 
nearly all principal and secondary species assume the tufted 
abit. An additional characteristic directly traceable to the 
“same conditions is the exceedingly long tap root developed by 
most sand hill inhabitants. The facies of the blue-stem forma- 
tion are Andropogon scoparius, Stipa comata, Calamovilfa longifolia, 
and Andropogon Hallii. The first is the most characteristic on 
‘count of the striking bunches which it forms. Stipa comaia is 
‘specially frequent and abundant. In certain situations, both 
ae toa considerable extent replaced by Calamovilfa longifolia, 
Andropogon Hallit, and even at times A. provincialis, all of 
Which except the last occur throughout the formation. The 
Scondary species are Eragrostis trichodes, Oryzopsis cuspidata, 
Mullenbergia pungens, Bouteloua hirsuta, B. oligostachya, Sporobolus 
| Yplandrus, and Cyperus Schweinitzit. Important modifications of 
his formation are imparted to it by the sand-cherry, Prunus 
Bisseyi, prairie rose, Rosa Arkansana, Amorpha canescens. Ceanothus 
watus and Yucca glauca. The number of secondary apeear ie 
great that only the most conspicuous can be mentioned : 
Sich are Cycloloma atriplicifolium, Froelichia Floridana, Erioghti™ 
amr, Chrysopsis villosa, Eriocarpum spinulosum, Opuntia hum ey 
tus viviparus, Psoralea lanceolata, etc. 
Aristida purpurea, 
e rarely Stipa 
h formations: Era- 
Aristida oligantha, 
more abundant 
es, in addition 
© pectinacea, Panicum Scribnerianum, 
Koelerig cristata and Eatonia obtusata are usually 
a beardgrass type. Of other secondary spec! 
