316 FRANCIS RAM ALE Y 



There are three common species in loose sand: Symphoricar* 

 pos vaccinoides, Rhus trilobata, and Ribes inebrians. Another, 

 perhaps best called an undershrub, is a species of rabbit-brush, 

 Chrysothamnus linifolius. 



Aside from grasses and sedges and a single species of rush the 

 herbaceous plants of sandy soil are all dicotyledons so far as 

 recorded. An annotated list including both shrubs and herbs 

 is given at the end of the paper. 



In the following account the vegetation is described under 

 four heads according to substrata: (1) Pure sand; (2) Sand-gravel 

 slopes; (3) Rock wash; (4) Rock ridges. Chief attention will be 

 given to plant associations on pure sand. 



1 . Plant communities on sand 



In areas of pure sand without rocks and with very little humus 

 there exist three distinct associations: (a) Shrub association, (b) 

 Wheat-grass association, (c) Short-grass association. Besides 

 these three definite communities various intermediate stages 

 are represented. The first two communities named are highly 

 primitive growths in soft, loose sand. Steepness of slope is an 

 important factor in determining their occurrence. The scrub 

 develops oftener on steep slopes and the wheat grass in more 

 level places. Scrub does, however, appear in some situations 

 where the ground is almost level. Short grass, even more than 

 wheat grass, needs level ground and it requires a soil that is 

 somewhat compact. 



a. The shrub association (or scrub) in loose sand is composed 

 of large circular growths of the various species. Most abundant 

 is Symphoricarpos vaccinoides. Chrysothamnus linifolius is also 

 common. Rhus trilobata and Ribes inebrians are of rather more 

 local occurrence. Three other shrubs occur chiefly where there 

 are rock fragments yet at times they too are found in pure sand. 

 These are Sericotheca dumosa, Cercocarpus montanus, and Oreo- 

 batus deliciosus. Among rocks, Sabina scopulorum and Juniperus 

 sibirica may be found locally in small numbers. In narrow gul- 

 lies there are the less xerophytic Prunus ??ielanocarpa, Grossu- 



