200 BOTANICAL GAZETTE [SEPTEMBER 
dry water courses and also all of the alluvial fans. Succession 
here is practically the same as on any ruderal area. In addition to 
Stipa Vaseyi there is usually found Boebera papposa, Salvia lanceo- 
lata, and in some cases Xanthium commune and Cleome serrulata. 
When the soil has become more stable Stipa Vaseyi slowly gives 
way. Artemisia frigida is now one of the first species to appear, and 
is often dominant after Stipa Vaseyi has disappeared entirely. This 
Me riol lix 
IG. 13.—Blow-out; the prominent plants are Muhlenbergia gracilis, 
serrulata, re emisia canadensis, and Andropogon scoparius; Calamov alfa longifolia 
in the background. 
is followed by Muhlenbergia gracillima, and after a number of yea" 
this is replaced in turn by Bouteloua oligostachya. 
On dry sandy ridges blow-outs are often found (fig. 13): 
succession here is usually Polygonella articulata, Cycloloma airipiicr 
jolium, Carex sp., Muhlenbergia gracilis, Sporobolus cry plandrus, 
Artemisia canadensis, Thelesperma gracile, Eriogonum annuum, 
Meriolix serrulata, Chrysopsis villosa, and Andropogon scopar ws. 
The 
