48 STUDIES IN THE VEGETATION OP THE STATE 



covered with a tbicket-like growth of Rhus, Corylus, Cornus, 

 and, lower down, Salix, scattered here and there with a few 

 large specimens of Populus. Several ravines of lesser im- 

 portance flow into this creek from either side. Through the 

 eastern and the western borders of this prairie, wide draws 

 pass from the south, tend northward, and empty into Table 

 creek.* The draw on the west broadens out, as it approaches 

 the creek, and loses itself, thus giving rise to a typical 

 meadow formation. On the east, the swale-like draw lies 

 at the foot of Great ridge and makes possible the one wet 

 meadow formation, which is in extent 400 x 100 meters. Im- 

 mediately after excessive precipitation, large volumes of 

 water from the surrounding region pass through these draws. 

 The above description, with a careful study of the contour 

 map, conveys a fairly accurate idea of the prairie formation 

 under discussion. The extreme diversity of elevation, the 

 various waterways, and the direction and degree of the nu- 

 merous slopes and exposures exert a pronounced influence 

 upon the other controlling physical factors, viz., light, soil 

 and air temperatures, and water-content. Since physio- 

 graphical factors, indirectly, produce favorable conditions 

 for one species and unfavorable conditions for another by 

 influencing the other physical factors, they are largely con- 

 trolling in the migration and distribution of species in a 

 prairie formation, as will be pointed out from time to time. 

 It can readily be seen that the ecological factors of light, soil 

 and air temperatures, and water-content exert a far greater 

 influence upon this formation than all other physical and 

 biological factors combined. The crests and southern ex- 

 posures of ridges maintain maximum soil and atmospheric 

 temperatures and light, while other slopes, northern and 

 eastern or western, maintain respectively minimum and 

 medium temperature and light Conditions. Northern sloi)e8 

 never receive maximum heat and light from the sun ; they are 



• Table creek for the most part is enclosed iar pasture, as the map indicatee, and henc» 

 will not appear in the discussion hereafter. 



