396 BOTANICAL GAZETTE [November 



Greasewood-white sage formation. — Pound and Clements 13, p. 374. 

 Chrysothamnus graveolens society. — Shantz 17, pp. 41, 47. 

 Bigelovia association. — Watson 20, p. 200, in part. 

 Greasewood society of the Bigelovia association. — Watson 20, p. 202. 



This growth occurs in deep alkaline soil which is usually more 

 or less loose or sandy. Chrysothamnus graveolens (Nutt.) Greene 

 (rabbit brush) is more abundant in loam; Sarcobatus vermiculatus 

 (Hook.) Torr. (greasewood) is more abundant in sandy loam or 

 sand; the two often dominate together. The lower slopes of the 

 two Table Mountains at Golden are covered with a Chrysothamnus 

 growth. Sarcobatus y with or without Chrysothamnus, is abundant 

 in sandy stream bottoms farther south in the valley of the Arkansas 

 River. With Chrysothamnus graveolens are often found Eurotia 

 lanata (Pursh) Moq. and Chrysothamnus plattensis Greene. An 

 open growth of the latter, usually mixed with the short-grass cover, 

 is frequent in low ground of draws, in which the soil is fine- 

 grained and with a high proportion of soluble salts, or on level 

 alkaline loose clay. 



Within the Boulder area these growths are local, and not par- 

 ticularly well developed. They range locally through the plains 

 region, and with similar growths, through the southwestern United 

 States. The present arrangement in one association of the par- 

 ticular growths seen is tentative. 



THE SALT-GRASS ASSOCIATION 6 



Salt-grass Or ache formation. — Pound and Clements 13, p. 388, in part. 



Two grasses, Sporobolus asperifolius (Nees and Mey.) Thurb. 

 and Distichlis spicata (L.) Greene, either together or singly, are 

 dominant plants in flats which are sometimes white with alkali. 

 Within the region such flats occur on gently sloping margins of 

 floodplain lakes and irrigation reservoirs, and in restricted stream 

 bottom areas. Irrigation, as at present practised, tends to increase 

 their number and extent. The soil may be clay or loam, is corn- 



flooding. 



trampled 



6 Vegetation of saline basins in the prairie region is discussed by J. H. Schaffner 

 in Notes on the salt-marsh plants of northern Kansas, Bot. Gaz. 25:255-260. 1898. 



