BOTANICAL GAZETTE 



[OCTOBER 



invariable bunch habit far the more conspicuous. A. scoparius 

 (fig. 4) seems to form a very loose sod between the bunches of the 

 former and extends lower down upon the slope, where in places it 

 yields to the Boutelouas or rarely to Poa. In succession these forms 

 seem to precede the Boutelouas. With a reduction of drainage 

 and introduction of these sod-formers, the bunch-grasses yield, and 

 in those portions of the prairie where succession has progressed most 



Fig. 3. — Autumnal aspect: the bunch-grass, Andropogon jurcatus, with interven- 

 ing spaces occupied by Bouteloua sod near crest of prairie knoll. 



rapidly, for example the northwestern exposure, the Andropogons 

 and the "bunch-habit" are conditions of the past. With Agropyron 

 occidentale, the Andropogons and Sporobolus must be ranked as the 

 pioneer grasses of the prairie, and as such hold a most important 

 ecological relation in the structure and development of the formation. 

 A. furcatus yields first, giving way to A. scoparius, which in places 

 assumes facial abundance and frequently persists in a somewhat 

 anomalous way in the more mesophytic associations. These grasses 



