Southeastern Washington and Adjacent Idaho. 55 



The June grass, Poa sandbergii, one of the pioneers of herba- 

 ceous vegetation in the moss consocies, is also perhaps one of the 

 most important interstitial plants of the prairies. It grows in 

 small tufts usually only about 0.5 to 1.5 inches in diameter but 

 as many as 30 to 40 of these may occur in a single minor quadrat 

 between the bunches of Festuca and Agropyron. It is called 

 June grass because of its habit of flowering in May or early June 

 and remaining dormant until the advent of the fall rains. This 

 means of evading drought is necessitated by its very shallow 

 root-system, which seldom exceeds 8 inches. Its xerophytic 

 tendencies are shown by its less abundance in mesophytic situa- 

 tions. 



The sod-forming habit of Agropyron spicatum in the prairies 

 of eastern Washington is in marked contrast to its well developed 

 bunch habit on the rim-rock or in the shallower and drier soils 

 westward. I have found the soil quite filled with rhizomes of 

 considerable length connecting smaller clumps of this grass. 

 It may well abandon this marked xerophytic character, for 

 its long roots extend into the fourth and fifth foot of soil, and 

 tap the earthen reservoir far below the root limits of competing 

 grass species. 



Another common bunch-grass, which, with the three preceding, 

 completes the list of dominant grass species, is Koeleria cristata. 

 Like Poa, the bunches are often small, but numerous. It com- 

 pletes flowering in early July and remains dormant until revived 

 by the autumn rains. Its well developed but short root-system 

 gets water from the first 15 inches of soil only. 



The entire absence of late blooming grasses, such as An- 

 dropogon, Sorghastrum, Bouteloua, and others of the prairie- 

 plains region, may be accounted for by the peculiar distribution 

 of the precipitation. 



A most characteristic plant of the prairies, and one which for 

 a time often outranks the grasses, is the prairie sunflower, Bal- 

 samorhiza sagittata (Fig. 42). Its abundance, size, and duration 

 all unite to make it a very important ecological species. It is not 

 unusual to find a dozen of these plants in an area of four square 

 meters. Only on the steeper northeast slopes and moist valleys 



55 



