128 MISSOURI BOTANICAL GARDEN 



into distinct regions by primary physiographic forces^ the 

 effect upon the flora must be far reaching. In the following 

 paper an attempt has been made to analyze the physio- 

 graphic features of the river valley and to study the distri- 

 bution of the local flora with reference to them. 



Since a cross section of the Mississippi River, following 

 a straight line laid down w^ith mathematical precision, would 

 not include the various features characteristic of the region 

 described, the cross section made is an ideal one, exempli- 

 fied in the accompanying diagram, embodying the principal 

 physiographic features of the region studied. The section 

 embraces, from east to west, the country lying between the 

 rolling prairies of southwestern Illinois on the one hand and 

 the Missouri plateau on the other, and includes portions of 

 the two plateaus. On the Missouri side the area covered 

 comi)rises the countrv between the mouth of the River des 



and 







side the territory is bounded on the north by 



drawn throuiih 



and 



east and west line drawn through a point about two miles south 

 of Falhng Spring, St. Clair county. 



In the collection of data for and in the preparation of this 

 paper the writer is indebted for valuable assistance to many 

 friends, in the first place to Professor AVilliam Trelease, at 

 whose smrerestion the work was undertaken. To Professor 



the 



Way 



Mr. J. J. Lichter, thanks are due for information along 

 geological lines, especially as far as borings in the American 

 Bottoms are concerned, and to Mr, J. H. Kellogg of the 

 Missouri Botanical Garden for numerous botanical data. 



PHYSICAL FEATURES. 



Meteorology, 



As pointed out by Clements,* unless meteorological readings 

 are taken in each habitat, they are of no value to the ecologist 



4 

 t 



* ClemcntSj F. E, Research Methods in Ecology. Lincoln. 1905. 



