54 A Study of the Vegetation of 
30 per cent. of the ground appearing bare by mid-summer. Closer 
investigation, however, reveals that much of this space was for- 
merly occupied by prevernal and vernal plants which have by this 
time become dry and brown. However, relict xerophytic mosses 
and lichens indicate the more open nature of the ground cover. 
A careful census of the plant population consisting of scores of 
list quadrats reveals striking differences, not only in the number 
of individuals, but also in the floristic distribution of species. 
On an average it was found that south slopes are clothed with 
about 115 individuals per square meter, while the north slopes, 
with only about 3 per cent. of unoccupied soil space, showed 
more than 200 individuals in the same unit area. 
Perhaps the most pronounced difference is the smaller number 
or total absence of more mesophytic plant-forms which thrive in 
moist situations. Erythronium grandiflorum, Trillium petiola- 
tum, Capnorea villosula, Vaccinium caespitosum, and Viola 
adunca are examples of species characteristic of moist north hill- 
sides. Numerous species, such as Sidalcea oregana, Circium 
foliosum, Valeriana edulis, Gentiana oregana, and others seldom 
occur on south slopes. 
The blue bunch-grass, Festuca ovina ingrata, ranking in im- 
portance with Agropyron spicatum, is the most characteristic 
grass of the region (Fig. 48). The slightly pale-green plants are 
densely tufted into bunches from 1 to 4 inches in diameter. The 
low, bushy, setaceous leaf blades scarcely exceed a height of 12 
inches. It is not unusual to find as many as 10 to 13 of these 
bunches in a single square meter. The bunch habit, an aspect 
of prairie vegetation which is found more or less developed in 
practically all prairie regions, and one which has succeeded in a 
remarkable degree in withstanding xerophytic conditions, is most 
pronounced on the drier slopes. In moist situations the clumps 
are smaller, but I have never found Festuca producing rhizomes. 
Like the other prairie grasses Festuca flowers by the middle of 
June. Since its root-system draws the water supply from the 
upper 18 inches of soil, its drying out in July and resumption of 
growth upon the arrival of the autumn rains can easily be ac- 
counted for. 
54 
