Manitoba and nearly all of Assiniboia and Saskatche- 
wan. 
-Plains,—west to'foot of Rocky Mountains and south and 
southwest to Sonora-Nevada desert. 
2. Prairie Formations. 
Tension line between forest and prairie not well marked, com- 
pare with skirmish line of armies—outposts. 
Climatic factors the dominant ones in limiting forest and 
prairie. 
I. Subordinate factors. 
a. Biotic, grazing of buffalo. 
D. ‘Physical, prairie! fires. 
2. Evident that climatic the dominant factor. 
a. Greater amount of rainfall is in spring and 
summer when grass most needs it. 
b. This is time when seeds.of trees would germi- 
nate and would die out in drought period. 
c. Firmness of soil and mat of grass hinder seed- 
ling getting a foothold. 
d. Heavy and drying winds in dry season and in 
winter cause excessive transpiration and scat- 
ter litter. 
Prevailing grasses in prairie region. 
Ist type. “Sod formers,’ long rhizomes, close formations. 
Ex. Drop seed (Sporobolus asperifolius). 
Koehleria cristata. 
Eatonia obtusata. 
Panicum scribnerianum. 
2nd type. Bunch grasses, tufts, tend to make open forma- 
tions. 
Ex. Buffalo grass (Bulbi:is dactyloides). 
Beard grass or broom sedge (Andropogon 
furcatus and scoparius ). 
Grama grass (Boutelo& oligostachya), etc. 
These two types are more or less mixed, but 
A Sod) formers, — iphaiie  vtacs) formation: 
characteristic of lower prairies. 
b. “‘Bunch’’ grasses characteristic of arid regions of 
steppes west and southwest. 
39 
