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 

 root, 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 densely in open, matlike patches, resulting 

 from a slow centrifugal migration through bulb formation coupled with 

 a 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 

 crests and Poa sod, where it exerts only a minor effect. The shallow 

 scaly brown bulbs indicate its perennial nature. Dissemination is 

 by propulsion, the few seeds formed being not distantly ejected from 

 the pentalocular ovary by the recurving of the loculicidally dehiscing 

 carpels. In this we have a still further explanation of its gregarious 

 tendency. 



Characterized by a general distribution, a subcopious abundance, 

 and the "bunch-habit" of growth which aggregates its many blue 

 and white flowers, Sisyrinchium angiistifolium becomes of first promi- 

 nence in the vernal floral aspect. It is perennial by short fibrous 

 rootstocks. It is abundantly fertile, and the smooth ovoid seeds are 

 discharged but weakly by the loculicidally dehiscing tricarpellate 

 capsule. 



