VOLUME XLVI NUMBER 2 
BOTANICAL GAZea ee 
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 I13 
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 Pounp 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- 
what to the west, with which it shows the closer floristic agreement. 
Its composition is thus twofold, pointing to the primitive and 
more xerophytic stages of the past and at the same time prophetic of 
the mesophytic stages to come. This aberrant character links it 
strongly to the xerophytic prairie to the west and southwest, from 
which it is genetically descended, and the prophetic character links it 
to the more mesophytic prairie of western Iowa, which has encroached 
‘ver westward. Under this migration tension from the southeast and 
€ast the primitive prairie has retreated, civilization always being 4 
potent factor in this succession. ; 
: Study began in this tri-state region in the fall of 1903 at Sioux 
City, Iowa, and was carried on during that fall and the next summer 
*Pounp, R., and Crements, F. E., Phytogeography of Nebraska. 1900. 
81 
