203] FLORA OF COLUMBIA AND VICINITY 6t 



Draba cuneifolia, and Alsine Texana are the chief species, with 

 the exception of Cladonia, which is often abundant in such soils. 

 Scutellaria campestris, S. parvula, and Astragalus distortus oc- 

 cur also. To these on the Pinnacles are to be added Mirabilis 

 hirsuta and Carex setifolia. 



B. Campanales. Plants of the prairie zone. 



In the vicinity of Columbia the true prairies are represented 

 only by a thin ribbon about the summits of cliffs, or upon the 

 summits of hills and bluflfs. Hence the prairie flora is found 

 growing mainly under xerophytic conditions. Such habitats, so 

 unlike those usual to the species, are plainly the result of con- 

 striction by the sylva of former prairies. Here in a soil of such 

 slight depth that trees and shrubs can find no foothold, a score 

 or two of species of prairie plants lead a precarious existence. 

 Besides there are a few prairie remnants in open thickets, wan- 

 dering about as conditions make necessary, or a few hardy ones 

 settling down in dense patches and battling stoutly against an 

 untoward fate. The most successful of these is the sensitive 

 brier (Schranckia uncin-ata). The prairie vegetation consists of 

 two associations, the one growing on the cliffs and mixed with 

 rupestrine forms, the other growing on hill-summits, or, as has 

 been seen, in open thickets. 



a. Campanales psoraleoides. The psoralea association 

 of cliff prairie plants consists largely of Leguminosae, Grami- 

 neae, and Compositac. It is mixed more or less with rupestrine 

 species, and in certain places coalesces with the flora of the red 

 clay barrens. The aestival plants consist mainly of Legumi- 

 nosae — Psoralea, Amorpha, Kuhnistera, Tephrosia, and Bap- 

 tisia; the autumnal of Gramineae — Andropogon, Bouteloua, etc. 

 Vernal species are scarce, consisting mainly of Astragalus Mex- 



