146 J. E. CRIBBS 



relative freedom from submergence, permits of a development of 

 vegetation far in advance of that occurring upon the lower 

 flood plains. 



Three general regions are distinguishable. Each bears a 

 definite relation to the stages of the river, and is characterized 

 by a typical flora. The three regions are: (1) the Littoral 

 Zone; (2) the Transition Zone, (3) the Upper Floodplain. 



The Littoral Zone. By the littoral zone is meant that part of 

 the plain immediately next the river, where there is a direct 

 effect upon the vegetation by the waters of the stream at its 

 ordinary levels. Locally this zone might well be subdivided into 

 three or four parts which bear the same relationship to each 

 other as do those of the lake successions. It is only in slow 

 streams or along protected banks that there is a considerable 

 development of submersed aquatics. When represented, the 

 chief components are Elodea, Nitella, Myriophyllum, Cerato- 

 phyllum, and Polygonum amphibium. The aero-aquatics and 

 floating aquatics are commonly more evident and include 

 Nymphea advena, Potomageton natans, Potomageton americanus, 

 Potomageton obtusifolius, Sagittaria latifolia, Scirpus validus, 

 Typha latifolia, Sparganium eurycarpum, etc. They occupy 

 the same relative position as in the lake series. Upon the banks 

 of the stream appear a few forms characteristic of this position, 

 such as Salix nigra, Acer saccharinum, Cornus stolonifera, and 

 Platanus occidentalis. Associated with these is commonly found 

 Mentha spicata, Lycopus americanus, Laportea canadensis, Poly- 

 gonum virginianum, etc. 



The Transitional Zone. The transitional zone may be well 

 defined or not but comprises the area submerged by the river 

 during periods of high water. It usually has a vertical eleva- 

 tion of from 4 to 10 feet above the normal level of the river. 

 To many forms the frequent inundation is detrimental, hence 

 they are excluded from this region. The species are largely 

 herbaceous and include Polygonatum mrginianum. Ambrosia 

 trifida, Lysimachia Nummularia, etc. Of the few shrub species 

 represented Salix and Cornus stolonifera, are most common in 

 occurrence. 



