60 A Study of the Vegetation of 



other plants are mat-formers, while a few are more or less 

 shrubby in character. 



The bunches of Agropyron are often 1-2 feet apart, perhaps 

 only 2-5 occurring in a square meter (Fig. 47). The individual 

 bunches or tufts are composed of from 100-350 or more stiff, 

 erect stems, reaching a height of 2-3 feet. Several generations 

 of dead stems are to be seen in these persistent bunches, the old 

 leaves and culms forming a tangle at the bushy base. Conse- 

 quently the landscape appears just as characteristic in late sum- 

 mer when this dominant is drying out as in the fall when it takes 

 on renewed growth, or in early spring when a host of inter- 

 stitials for a time cover the ground with a green carpet. Agro- 

 pyron is the one grass best adapted for such situations. Its well 

 developed roots penetrate the moist crevices in the underlying 

 basalt to a depth of 4 or 5 feet. 



Grasses like Festuca ovina ingrata and Koeleria cristata with 

 rather short root-systems find this an uncongenial habitat. How- 

 ever, a few grasses with very short root-systems and an early 

 blooming habit are very successful interstitials. Of these, Poa 

 sandbergii and the low annual, Festuca pacifica, are by far the 

 most important. Hundreds of individuals of the latter fre- 

 quently occur in a single square meter. Mats of Antennaria 

 dimorpha and dense growths of Plantago purshii are likewise 

 common between the scattered bunches of the dominant. These 

 interstitials, together with numerous others are quite as common 

 in the preceding Poa-Polygonum associes of which this, indeed, 

 except 'for the dominance of Agropyron, might be considered a 

 late developmental stage. However, the presence of the rabbit 

 brush, Chrysothamnus nauseosus, C. viscidiflorus, Tetradymia 

 canescens, Erigeron hispidissimus, and various lupines, espe- 

 cially in pockets of deeper soil, indicates the developmental trend 

 toward the more typical Agropyron community. 



In the deep soils of the hills bordering the scab-lands the Agro- 

 pyron consociation is better developed (Fig. 20). The appear- 

 ance of Festuca ovina indicates more favorable life conditions. 

 Indeed, the latter sometimes assumes equal importance with 

 Agropyron on the more moist slopes. But the larger amount of 



60 



