THE PEAIRIES 225 



degrees of fixation aud topography, and among those growing in 

 more exposed places 123 species are also more or less common on 

 the prairies of western Iowa. Of the 12 "dry- valley" species 

 (p. 140) 9 are common prairie plants, and 8 of the 27 "blowout" 

 species (p. 139) are of the same type.-- 



In these cases the prairie flora cannot be due to fineness of soil, 

 for it grows here in sand of varying coarseness; rainfall and 

 other general meteorological conditions cannot be responsible, for 

 adjoining surfaces are frequently covered with a mesophj'tie for- 

 est ; and fires and earlier grazing or tramping of bisons are out of 

 question as the dunes frequently present a flora too scant for 

 either cause. 



These sandy areas are xeroph\i:ic, and the inevitable conclusion 

 is that the prairie flora largely takes possession of them only 

 because it is xeroph^iiic and can exist here as well as on the xero- 

 pliytic surfaces of ordinary prairie."^ 



-- That a large part of the flora of sandy areas consists of prairie 

 plants is also confirmed by Gleason's paper on "The Vegetation of the 

 Inland Sand Deposits of Illinois ' ', Bulletin of the Illinois State Labora- 

 tory of Xatural History, vol. IX, 1910, pp. 23-174, which was received 

 after this paper was written and the greater part of it had been printed. 

 The author lists Acerates viridiftora and its varieties, and Litliospermum 

 GmeJini, Euphorbia coroUata, and Lespedeza eapitata as characteristic of 

 the blowout basins. All are conmion prairie plants in Iowa. Of the 31 

 species listed in the blowsand association (pp. 93-94) those belolnging to 

 the genera Ambrosia, Cassia, Oenothera (2 sp.). Euphorbia (2 sp.), 

 Hedeoma, Lepidium, Lespedesa, and Seutellaria, ten in all, are common 

 prairie types, and those belonging to CommeJina, Cenchrus, Tephrosia, 

 Cycloloma, and Festuca also occur on prairies, though more frequently 

 on sandy areas. The transect across a blowout (p. 101) shows 14 species, 

 of which Bouteloua hirsuia, Lespedeza eapitata. Ambrosia psilostachya, 

 Panicum virgatum, Equisetum laevigatum and Koeleria cristata are typ- 

 ical prairie plants, and Festuca octoflora is sometimes found on the prairie. 

 Most of these plants are more common on dry prairies, but extend to 

 prairies of all types. 



23 In order that there may be no misunderstanding as to the scope of 

 this statement attention is called to the fact that in the region here un- 

 der discussion even the most fertile prairie becomes xerophytic during the 

 prevailing average late-summer conditions, and that frequently areas, 

 which are quite wet during a part of the year may be reduced to the same 

 condition at this time. Often the dryness of the air produces a marked 

 effect before the lack of free soil-water has reached the danger point. It 



