An associational study of Illinois sand prairie . al type ofvegetation; we may thus speak of forest or grassland animals just aswe speak of forest or grassland plants. The climate of Illinois favonithe growth of the deciduous forest (Gleason, 1910: 117; Schimper, 1903:162-175; Transeau, 1905). The sand-prairie has been enabled to per-sist only through the presence of local conditions of aridity. The edaphic factors to bo considered in any regional study areheat, light, water and humidity, wind, soil, and topography. Theseedaphic factors make up v/hat might be called an environmental complex;th
An associational study of Illinois sand prairie . al type ofvegetation; we may thus speak of forest or grassland animals just aswe speak of forest or grassland plants. The climate of Illinois favonithe growth of the deciduous forest (Gleason, 1910: 117; Schimper, 1903:162-175; Transeau, 1905). The sand-prairie has been enabled to per-sist only through the presence of local conditions of aridity. The edaphic factors to bo considered in any regional study areheat, light, water and humidity, wind, soil, and topography. Theseedaphic factors make up v/hat might be called an environmental complex;they are so closely interrelated that they cannot readily be analyzedand classified. It might be well to include them all under the termphysiography, for local environmental conditions are primarily mat-ters of physiography. The most important physiographical feature ofthe region studied is the soil. Sand has peculiar physical and chem-ical properties, which greatly influence the other edaphic factors may nov/ be discussed in Temperature variations in sand from day to night and from thesurface to the subsoil are great. When the association is open, asit usually is, the insolation is heightened by reflection; heat andlight are thus both intense (Gleason, 1910: 34). The moisture relations of sandy soils are peculiar. Coarse-grained soils hold relatively small amounts of vyater; on the otherhand, more of this water is available to plants than in fine-grainedsoils. Coarse loose soils dry very readily at the surface; there isa compensating tendency here, too, as the dry surface layer forms amulch which retards further evaporation, sc that there is alv/ays con-siderable moisture in the sand a few inches below the surface. The more amount of evaporation therefore depends^upon the degree of opennessof the association than upon the kind of soil. The amount of evapo-ration depends upon (T. Russell, 1888) the temperature of the evapo-rating surface, the relative humid
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