VOLUME XLVI NUMBER 2 



Botanical Gazette 



AUGUST 1908 



FLORAL SUCCESSION IN THE PRAIRIE-GRASS FORMA- 

 TION OF SOUTHEASTERN SOUTH DAKOTA 



THE PREVERNAL, VERNAL, AND ESTIVAL ASPECTS 

 CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY II3 



LeRoy Harris Harvey 



(with three figures) 

 The western part of Iowa, the eastern and northeastern counties 

 of Nebraska, and southeastern South Dakota lie in the drainage basin 

 of the Missouri. This tri-state area is well within the prairie region 

 of that vast and far-reaching prairie province of the middle west. 

 This area is only a part of the Ponca District of Pound and Clem- 

 ents,^ being more strictly Dakotan than Nebraskan, and may be 

 considered as representing a transition between the more meso- 

 •^ phytic eastern areas of Iowa and those dominantly xerophytic some- 

 V5 >: what to the west, with which it shows the closer floristic agreement. 



- SJ Its composition is thus twofold, pointing to the primitive and more 

 ^ tf xerophytic stages of the past and at the same time prophetic of 

 ~ ^ the mesophytic stages to come. This aberrant character links it 



- 2 strongly to the xerophytic prairie to the west and southwest, from 



- s which it is genetically descended, and the prophetic character links it 

 : ^ to the more mesophytic prairie of western Iowa, which has encroached 



^ ever westward. Under this migration tension from the southeast and 

 east the primitive prairie has retreated, civilization always being a 

 cz> potent factor in this succession. 

 P^ Study began in this tri-state region in the fall of 1903 at Sioux 



i City, Iowa, and was carried on during that fall and the next summer 



' Pound, R., axd CLEiDEXXS, F. E., Phvtogeographv of Nebraska. 1900. 



< 



