1908] HARVEY— PRAIRIE-GRASS FORMATION 281 



45 cn \ which however may frequently reach 60 to 8o cm , 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 enlarged 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 slope? 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 

 this 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 8o cm and are terminated by cylindrical 

 spikes (some 8 or 9 cm long) of white flowers in K. Candida and 

 (some 5 cm 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 

 Lygodesmia juncea. Eriocarpum is perennial from a deep woody 

 root, whose much-branched stems rise about 30 to 4o cm , terminate 

 in 1 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 

 crests precludes more than a minor influence upon the tone. It 



