36 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



In the mixed-prairie quadrat the dominance of the short-grasses, 

 Bouteloua gracilis especially, but also some Muhlenbergia gracillima, 

 and the grass-like Carex pennsylvanica, is at once apparent. This is 

 due to the close grazing over the area previous to the establishment of 

 the station. This likewise accounts for the abundance of Aristida 

 purpurea (a plant eaten by stock only when other vegetation is scanty) 

 the growth of which has been favored by the close grazing of its compet- 

 itors. However, the real mixed-prairie nature of the vegetation is 

 revealed by the frequent occurrence of Andropogon scoparius and the 

 presence of Kceleria cristata and Bouteloua curtipendula, representing 

 the tall-grasses. Although careful mapping reveals a considerable 

 bare area, a condition which indicates a low water-content, and one 

 usually underestimated in a casual survey, still the presence of Arte- 

 misia frigida, Chrysopsis villosa, Lithospermum linearifolium, Psoralea 

 tenuiflora, and other subdominant herbs indicates a sufficient supply 

 for both herbs and grasses. The absence of Plantago purshii, Sched- 

 onnardus paniculatus, and other ruderal or semi-ruderal species indi- 

 cates that the vegetation is stable and has suffered no serious disturb- 

 ance. Since inclosed in 1918, the tall-grasses and herbs are rapidly 

 gaining in importance in the short-grass turf. 



The quadrat on the hilltop in the true prairie (fig. 1 1 and plate 5, a) 

 is typical for upland conditions. Andropogon scoparius, Kozleria 

 cristata, Bouteloua curtipendula, and Stipa spartea with Carex pennsyl- 

 vanica occur rather abundantly throughout. Andropogon furcatus and 

 A. nutans, both more typical of low prairies, occur only sparingly and 

 are associated with Poa pratensis. The grouping of these three less 

 xerophytic plants in one portion of the quadrat and the presence of 

 Bouteloua gracilis in another indicates differences of an edaphic nature. 

 When field studies become more intensive, such differences may be 

 readily understood. Constant differences in available water have not 

 infrequently been found at stations only a few feet apart. Local 

 areas of the shorter grasses are frequent on prairie ridges, but they are 

 seldom of great importance. The large number of individual plants 

 or clumps of plants in the area (over 215), the intimate mixture of so 

 many other herbs, and the closed nature of the vegetational cover are 

 all indicative of the more favorable growth conditions. This is further 

 indicated by the presence of certain species (Oxalis stricta, Poa pratensis, 

 etc.) which do not occur in the drier areas westward, but especially by 

 the greater height growth and leaf development of plants like Kceleria 

 cristata and Bouteloua curtipendula, which are found throughout both 

 grassland communities. A further statement of the development of 

 mixed-prairie vegetation, and especially of root systems, may be found 

 in Chapter IV (c/. Chapter IV, and particularly plate a in "Ecolo- 

 gical Relations of Roots")- 



