516 Part IV. Chapter 3. 
rosettes. The chief moss is Gymnostomum curvirostre , the lichens are Parmelia capitata, 
Physcia stellaris and Peltigera rufescens and the ferns are Cheilanthes lanuginosa, Pellaea atro- 
purpurea, Woodsia obtusa. During the summer the cliff flora is augmente by Hypericum 
maculatum, Linum virginicum, Pimpinella integerrima, Sporobolus asper, Aster oblongifolius, A. 
novae-angliae, Solidago Drummondi, S. ulmifolia. The top of the bluff is oceupied mainly 
by Panicum depauperatum, Androsace occidentalis, Rudbeckia hirta, Desmodium marylandicum, 
D. paniculatum, Psoralea tenuiflora, Stylosanthes elatior, (= S. biflora) and in patches the lichen 
Cladonia fimbriata. 
Prairie Formation. In the vicinity of Columbia, Missouri, according to 
DANIELS, true prairies are represented only by a thin ribbon of vegetation 
about the summits of cliffs, upon the tops of hills and bluffs or in open thickets. 
It is, therefore, a portion of the true prairie flora that is interdigitated 
with the forest formations of the Ozark Area and in a soil of such slight dept 
that trees and shrubs can find no foothold, this remnant of a prairie flora 
leads a precarious existence. The most successful plant in the struggle is 
Schrankia (Morongia) uncinata. The cliff prairie grasses are Andropogon fur- 
catus, Chrysopogon avenaceus, Panicum virgatum (rare), Bouteloua racemosa, 
Agropyrum spicatum (rare). 
Chapter II. North American Temperate Zone: Xerophyti6 
Section of the Interior. 
1. Prairie Region. 
The origin ofthe American prairies has long been a favorite theme 
for discussion among physiographers and botanists. The general concensus 
of opinion has been that fires have played a prominent part in their formation. 
Other theories advanced have had adherents, the cause of prairies being traced 
to the fineness of the loess, the direction of the strong prevailing southwest 
winds, inimic to tree growth; the occupancy of a recent submerged area by 
grass vegetation after the recession of the water; the peculiar chemic character 
of the soil; the character of the climate; the underlying geologic formations, 
rainfall, etc.’). It seems, however, to the writer that none of these theories 
adequately express the reason for the origin of prairies, but that the ex- 
planation is to be sought in phytogeography, not in geology, meteorology, es 
The soil, the climate, the underlying geologic formations are all favorable to 
tree growth. The prairie soils, however, originating as loess, were at once 
tenanted by grass vegetation, because in proximity in nearby plant formations. 
Royal Geographical Society new ser. 1893, 78—ı00. MerHan, TuoMas: Treeless Prairies, 
Botanical Gazette VI: 253. Topp, J. E.: Distribution of Timber and Origin of Prairies In Tom 
American Naturalist 1878. : 91, Hay, O. P.: An Examination of Prof. LEO LESQUEREUX 3 
a 
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