1908] H{1ARVEY—PRAIRIE-GRASS FORMATION 281 
45°, which however may frequently reach 60 to 80°, and is the 
only species which becomes at all conspicuous. These species as they 
enter the open bunch-grass association form mats, which fusing form 
sod, finally resulting in the replacement of the bunch-grasses. The 
gramas are all perennial by means of the eniarged rootstocks. : 
Coincident with the flowering of the grasses is that of Kuhnistera 
purpurea, which seems to precede that of its related species K. 
candida by only a few days. The purple Kuhnistera is from its 
distribution and structure more xerophytic than the white-flowered 
Species. The former occurs most abundantly on the higher slopes, 
decreasing in abundance downward ; while the latter reaches its 
maximum abundance on the lower slopes, decreasing in the number 
of individuals per unit area upward. Along middle slopes the 
abundance of the two species approaches equality. Its distribution 
seems clearly related to the chresard of these various habitats. CLEM- 
ENTS (’05, pp. 233) in light of these facts has suggested the mono- 
Phyletic origin of these two species from an ancestral form which 
became split up into purpurea and candida. under the influence of 
and adaptation to a low and high chresard, a xerophytic and meso- 
phytic habitat respectively, and has instituted experiments to test 
theory. In their respective positions of maximum abundance 
each may rise to dominance, which, however, never occurs in the plot 
under study; the advanced condition of the prairie seemingly pre- 
cludes such abundance in the closed association. However, they are 
the most conspicuous elements of the early part of the aspect. Their 
branching stalks rise 60 to 80°™ and are terminated by cylindrical 
Spikes (some 8 or 9°™ long) of white flowers in K. candida and 
(Some sem long) of violet flowers in K. purpurea. They are perennials 
from thick and deep roots. The seeds are immobile, which with the 
Perennial root accounts for their somewhat even distribution in the 
formation. 
: With the prairie clovers appear Eriocarpum spinulosum and 
godesmia juncea. Eriocarpum is perennial from a deep woody 
Foot, whose much-branched stems rise about 30 to 40°™, terminate 
nes 2 to 25 heads fringed with yellow rays and 2.5°™ in diameter. In 
all it is Very striking, but its rare occurrence along upper slopes and 
“tests precludes more than a minor influence upon the tone. It 
