270 FRANCIS RAMALEY 



periods are recognized: (1) Prevernal, May 1 to June 15, char- 

 acterized by the blooming of Mertensia bakeri and Thlaspi 

 purpurascens; (2) Vernal, June 15 to July 1, with Cerasiium 

 occidentale, Carex stenophylla and various species of Antennaria 

 in bloom; (3) Early Aestival, July 1 to July 15, during which 

 there is a profusion of flowers, particularly Aragallus lambertii, 

 Antennaria anaphaloides, A. rosea, A. microphylla, Comandra 

 pallida, Sedum steyiopetalum, Eriogonum umhellatum, etc.; (4) 

 Later Aestival, July 15 to August 1, showing blossoming of many 

 grasses, Festuca, Poa, Koeleria, Bromus, Agropyron, also the 

 species of Artemisia and Campanula petiolata and Orthocarpus 

 luteus; (5) Autumnal, August 1 to October 1, during which 

 time there occurs the blooming and fruiting of Muhlenhergia 

 gracilis, the most abundant grass of the park, together with the 

 flowering of a blue gentian, Dasystephana parryi. A series of six 

 societies or aspects is noted, corresponding to historical stages 

 from bare soil to the ultimate grassland of the park; other socie- 

 ties, not in the main line of succession, are also characterized. 

 A brief section on environmental factors discusses climate, soil, 

 evaporation, importance of ground squirrels, etc. Accounts 

 are presented of geographical relations, duration of individuals 

 and underground parts of plants. The paper closes with a list 

 of 133 species belonging to the dry grassland, a special desig- 

 nation being made of the 36 most important. 



