1 



AN ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI RIVER 



IN THE REGION OF ST. LOUIS, MISSOURI.* 



BY HENRI HUS. 



INTRODUCTION. 



^ 



The diversity of physiographic conditions afforded by a 

 great river like the Mississippi always offers an incentive to a 

 study of the distribution of the vegetation about it. This 

 is particularly true of the Mississippi in the region of St. 

 Louis, Mo. Here it traverses a valley from four to eight miles 

 broad of which a portion, approximately one mile in width, 

 is occupied by the stream. The greater part of its alluvial 

 flood plain Ues in Illinois, there forming the most northern 

 portion of the American Bottom. This flood plain is modi- 

 fled by numerous agents either natural or artificial. Bodies 

 of water, varied in extent, occupy a large area. While some 

 of them are connected with the river at all times, others are 

 so only in times of flood. Creeks, descending from the pla- 

 teau, cut their way to the Mississippi. The land itself is 

 high or low, sandy or clayey. Portions of it have been 

 diked. Wooded tracts have been denuded for agricultural 

 purposes. The resulting diversity of vegetation finds a paral- 

 lel in that of the plateaus of Missouri and Blinois, both origi- 

 nally forming part of the same peneplain. These plateaus 

 have been modified by various physical agents. Water is 

 responsible for the formation of ravines and sinkholes. 

 Under the influence of man large portions of the original 

 forest have disappeared. Farms now occupy their place. 

 Naturally these influences have gone far to modify the original 

 vegetation. Contemporaneous with the recession, or even 

 disappearance, of a species is the advent and cstabhshmcnt of 

 another. Railroads, bringing about entirely new conditions, 

 have offered favorable opportunities for the development and 

 distribution of certain species, at the same time assisting in 

 the immigration of others. It is realized that where the 

 secondary influences act upon a country already modeled 



A thesis presented to the Faculty of Washington University, in 

 candidacy for the degree of Doctor of Philosophy, April. 1908. 



(127) 



