COLOGICAL CROSS SECTION OF THE MISSISSIPPI. 



1S7 



covered by a thicker or thinner layer (0-12 in.) of mud 

 which apparently supports no vegetation. There is a slight 



accumulation of c 

 and broader zone, 

 level of the river, 

 yards. The lowei 



This is followed by the third 



summer and 



from 



by 



one 



[by Cy peril s 



acuminatus, C. diandrus and Fimbnstylis autumnalis. Separ- 

 ated from this by a strip of bare mud, about a foot in width, 

 lies a strip about 12 inches wide, covered by dwarf plants of 

 Coreopsis aristosa mutica. A third strip, again placed at 

 about one foot distance and as broad, contains nothing but 

 seedlings of Saliz longifoUa, from two to three feet high, inter- 



spersed with seedlings 



and 



7 



Here occasionally a rosette of Capsella 



tons is seen. Numerous are small fronds of Ricda natans. 

 The second part of this third zone, from fifteen to thirty-five 

 yards wide, contains rosettes of Capsella Bursa-pastoris 

 only, the rosettes being placed at some distance from each 

 other. The upper portion of the third zone, situated con- 

 siHornhhf Viio-lipr thnn the rest, shows small plants of Nas- 



turtium obtusiim, N 

 misia ludovicianay 



Jasdculat 



carolinianum, Arte- 

 Samolus Valerandi 



americanus, Ipomoea purpurea, Solanum nigrum, Conobaea 

 multifida, Lippia lanceolata, Acnida tuherculata, Rumex 



crUpus and R. maritimus, Polygonum aviculare 



hydro- 



pipcroides and P. Persicaria, as well as the plants of the 



middle zone. Here 



of Lactuca 



and L. Scariola integrata as well as rosettes of Daucus Carota. 

 In autumn rosettes of Juncus tenuis, at first sight readily 

 mistaken for Isoetes, are numerous. In this zone belong the 



8 



und in the small 

 numerous, formin 



This 



middle 



As is but 

 Ingly variable nature. 



rywhere may 



described be found so clearly defined. In places the upper 

 zone is but narrow, the current of the river having been de- 

 fleeted by an obstruction at some distance. As a result 



