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points. Submerged and fioating plants are absent or unimportant. Below 
the sewers, Oscillatoria is the only form found. Above them, Cladophora, 
Hydrodictyon and Potamogeton pectinatus occur. Neither Nymphea 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 levis, 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 HEupatorium perfoliatum. Other spe- 
cies are Apocynum cannabinum, Bidens frondosa, Xanthium canadense and 
Verbena urticefolia. The final stage is represented by Salix nigra, Plata- 
nus occidentalis, Vernonia noveboracensis and Aster nove-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 levis. 
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. 
Hydrophytie 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 floed-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 by the following typical list of species: 
[16—26988 | 
