Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 255 



varies from three or four inches to several yards. Quite naturally 

 when these intervals become great the presence of the true short- 

 grass condition becomes emphatic, and this appears to be one of the 

 reasons w^hy Shantz has included this as one of the short-grass asso- 

 ciations. The more open character of this association as it occurs 

 with us, which is well indicated by the number of secondary species, 



Fig. 14. Wire-grass, Aristida longiseta. Plant, showing habit, 

 a; spikelet, b; flowering glume, c. (From Shantz.) 



Stands in sharp contrast to the closer association as seen in the 

 typical expression of the short-grass formation. 



Toward the northern and eastern portion of the sandhill region 

 Aristida purpurea and A. basiramea are the usual controlling species 

 of this association. On the southwestern border Aristida longiseta 

 is the commonest species seen in the association where it comes in 

 closest contact with the short-grass formation. 



