Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 225 



species occur within the bunch-grass association they are therefore 

 to be regarded as reHcts. Indeed these species do not always pre- 

 sent the bunch-grass habit, and whenever this tendency appears the 

 bunches are small and the number of component stems much fewer 

 than is the case with Aiidropogon scoparius. 



At stations in the central and eastern portions of the hills these 



Fig. 10. Big bluestem, Andropogon hallii. Clump, showing 

 habit of growth, a; single plant, b; details of 

 spikelet, c, d, e, f. (From Shantz.) 



species become (as reported by Pound and Clements) locally con- 

 trolling at certain seasons of the year. Thus during early summer 

 the bunch-grass association may be quite distinctly modified by the 

 presence of Koeleria cristata and Stipa comata. Such areas, usually 

 indicative of a firm soil, are to be regarded as plant societies which 

 for a certain time more or less mask the background of Aiidropogon 



