1908] HARVEY—PRAIRIE-GRASS FORMATION 95 
gressively during the second week of the aspect, and together produce 
a very noticeable change in the floral tone, a change which is further 
accentuated by the forms that occur later. The yellow tone given 
by the puccoon becomes dotted here and there by yellow, blue, violet, 
white, and purple, and a bizarre tone is the result. Castilleja occurs 
rarely and of a very restricted distribution, being confined to associa- 
tions upon upper slopes, where its pale-yellow flowers render it always 
inconspicuous. The thickened perennial roots are parasitic upon 
the roots of other plants. Many flowering stalks may arise from one 
toot, thus assuming a bunch habit. The high immobility of the 
seeds, resulting in a very restricted distribution, accounts for its 
gregarious habit and local occurrence upon the prairie. 
Viola pedatifida with its bright-blue flowers and unrestricted dis- 
tribution and sparse to subcopious abundance exerts a characteristic 
effect on the vernal tone. The prairie violet is a perennial from a 
fleshy short rootstock. 
Oxalis violacea seems somewhat restricted to middle and lower 
slopes, where it may occur denscly in open, matlike patches, resulting 
from a slow centrifugal migration through bulb formation coupled with 
: positive ecesis, Though acaulescent and of low stature, its grega- 
rious habit and rose-purple flowers, with their green background of 
palmately trifoliate leaves, make it-in restricted plots of primary floral 
importance in the aspect. It likewise occurs sparsely but generally 
distributed over all parts of the formation, with the exception of 
‘rests and Poa sod, where it exerts only a minor effect. The shallow 
ei brown bulbs indicate its perennial nature. Dissemination is 
ie pi the few seeds formed being not distantly ejected from 
a. a ocular ovary by the recurving of the loculicidally dehiscing 
- In this we have a still further explanation of its gregarious 
y. 
oe btagae by ' general distribution, a subcopious abundance, 
and whit eneh-habit’” of growth which aggregates its many blue 
nence ; € towers, Sisyrinchium angustifolium becomes of first promi- 
Clea vernal floral aspct. It is perennial by short fibrous 
OCKS. It is abundantly fertile, and the smooth ovoid seeds are 
di 
ot but weakly by the loculicidally dehiscing tricarpellate 
