241 



points. Submerged and floating plants are absent or unimportant. Below 

 the sewers, Oscillatoria is the only form found. Above them, Cladophora, 

 Hydrodictyon and Potamogeton pectinatus occur. Neither Nymphoea nor 

 Castalia is found, probably because of sewer contamination, together with 

 the rocky character of the bottom. 



At a number of points, distinct zonation occurs. The succession may 

 be described as composed of five stages, the first of which is always domi- 

 nated by Sagittaria. Typha makes up the second stage, and is followed 

 by Bidens Isevis, which forms the third stage. Where zonation occurs this 

 Bidens zone is always very definite, and usually extends from the edge of 

 the water back two to ten feet. The fourth stage is represented by a zone 

 dominated by Ambrosia trifida and Eupatorium perfoliatum. Other spe- 

 cies are Apocynum cannabinum, Bidens frondosa, Xanthium canadense and 

 Verbena urticsefolia. The final stage is represented by Salix nigra, Plata- 

 nus occidentalis, Vernonia noveboracensis and Aster novje-angliie. 



Where all five zones occur, they are very closely crowded together. In 

 one instance all were clearly defined in a space of about fifteen feet. Tele- 

 scoping of stages is common. In two instances, young willows were found 

 in the midst of the zone of Bidens Isevis. 



The black willows form a very conspicuous feature of the floor of the 

 gorge. They occur commonly in definite lines which parallel the stream at 

 a distance of ten to fifty feet. A very striking example of this occurs 

 just below the Starr piano factory, on the east side of the river. Other 

 lines of trees of this species occur in similar locations farther down the 

 river. 



Hydrophytic flood-plains of the usual kind occur commonly in the 

 floor of the gorge. These may be so low as to be covered by the river 

 at every slight rise, or they may be above the level of the highest flood 

 stage. At the main bend of the river lies a high flood-plain of very con- 

 siderable size. Low hydrophytic flood-plains lie on both sides of the 

 stream immediately at the Starr piano factory. These are narrow, being 

 only a few feet in width at some places. These show a very characteristic 

 vegetation, as shown Ijy the lljllowing typical list of species: 



[IG— 269SS] 



