256 FRANCIS RAMALEY 



slightly less xerophytic than the preceding, most often devel- 

 oped on flats or gentle slopes with coarse soil and little humus. 



3. Muhlenbergia-Comandra society. Muhlenbergia gracilis, Co- 

 mandra -pallida, Arenaria fendleri, Antennaria arida, A. aprica 

 and A. microphylla, Carex stenophylla, Aragallus lambertii, 

 Koeleria cristata. Chiefly on slopes exposed to the west wind. 



4- Muhlenbergia- Antennaria society. Muhlenbergia gracilis, 

 Koeleria cristata, Antennaria anaphaloides, Arenaria fendleri, 

 Carex stenophylla, Aragallus lambertii. Throughout a large part 

 of the season the white inflorescences of Antennaria anapha- 

 loides make this grouping of plants conspicuous (fig. 2). Like 

 the preceding society this one occurs chiefly on exposed slopes 

 and knollsides. There is usually a moderate amount of humus 

 in the soil. 



5. Muhlenbergia- Aragallus society. Muhleyibergia gracilis, Ara- 

 gallus lambertii, Arenaria fendleri, Antennaria spp., Carex fili- 

 folia, Koeleria cristata, Poa crocata and P. rupicola. The soil 

 is much the same as that of the Muhlenbergia- Antennaria society 

 but, as already noted in the account of seasonal aspects, this 

 society develops most often on slopes not exposed to the severest 

 winds. 



6. Muhlenbergia-Danthonia society. Muhlenbergia gracilis, Dan- 

 thonia parryi, Festuca saximontana, Poa interior, Carex fili- 

 folia. Essentially a grass society with few dicotyledonous plants 



(fig. 4). 



These six societies are listed in order of water requirements. 

 The first is hyperxerophytic, being found only on dry coarse 

 soil and usually in places exposed to rapid evaporation. The 

 sixth develops on soil having some considerable amount of humus. 

 Nos. 2, 3, 4, and 5 are intermediate types; botanists disposed to 

 "lump" might put them all together, or perhaps consider them 

 as subsocieties. No doubt our serial itrrangement suggests 

 with a fair degree of accuracy the historical succession of the 

 various societies from their first origin on dry morainal gravel 

 or dry stream terraces. In passing from our No. 1 to No. 6 

 some may be left out. 



Abandoned roads or trails through the dry grassland grow up 



