44 THE RELATION OF PLANTS TO TIDE-LEVELS 
The blooming of the Spartina on the west shore shows the same features that 
have been noted in plants growing on the Spit. 
The largest areas within the boundaries of this part of the Spartina belt that 
are not covered more or less densely by this grass are the beds of the fresh-water 
streams entering the harbor on the west side. The more important of these are 
indicated on the map. Wherever any considerable rivulet runs down over the 
beach it cuts the Spartina belt clear across by washing off the peaty mud down 
to the underlying gravel. ‘The smaller of these channels, running across the 
beach, are but a decimeter or two in width, while the larger ones may bare the 
gravel for a width of 1, 2, or rarely 3 meters. On the edges of these channels 
the firm mud, on which the Sparta grows, stands at a level of 2 to 4 dm. above 
the bed of the rivulet. On the edges of these steep banks the Spartina stops 
abruptly, just as we have seen it do along the tide-stream in the southeast 
corner of the harbor. This is also much the way the stand of Spartina ends 
about the reentrant notches along its ragged outer border. Such notches are 
found especially along the west shore. On the projecting points of the dissected 
edge of the Spartina area, however, the firm peat slopes off gradually to the 
soft mud of the harbor bottom, and here the Spartina does not stop abruptly, 
but thins out rather gradually. Much of the raggedness of the outer edge of the 
Spartina belt is probably due to the burrowing through the substratum of the 
muskrat (Fiber zibethicus). 
The stand of Spartina along the west shore is practically pure up to the 
6-foot level. The only other plants commonly occupying the bottom between 
these levels are the gelatinous or felted green and blue-green alge, with 
occasional tufts of Ascophyllum and tangles of Pucus. On two small areas close 
together at 1,845 north and 1,860 north a few hundred plants of Lile@opsis were 
found between the 6 and 6.5 foot levels (plates x1r and xx11). As in the case of 
the LInleopsis found in the southeast corner of the harbor, these also seem to be 
- associated with fresh water. In these particular areas on the west shore there is 
no fresh water running over the surface, but if a stake is pushed into the soft, 
spongy mud and withdrawn, the water collecting in the hole is entirely fresh to 
the taste. Moreover, there is fresh water seeping out to the surface 3 or 4 meters 
down the beach, and forming a tiny rivulet from the 5-foot level downward. 
The only place about the harbor where Lil@opsis is not evidently associated with 
fresh water is at 60 north by 1,050 east, where, however, it is just beside the tide- 
stream, the water of which is only brackish, at the surface, at the time it covers 
the area in question. 
On the west shore, as on the east side, the upper boundary of the pure growth 
of Spartina glabra is less regular where the beach is shaded or saturated with 
fresh water. The plants succeeding the Spartina at its upper limit are different 
as these conditions differ. The three species with which Spartina is most often 
mingled at its upper margin, and by which it is displaced slightly higher up, 
are Spartina patens, Distichlis spicata, and Scirpus americanus. 
In regions where the beach is gently sloping, and well drained between the - 
6 and 8 foot levels, S. glabra is usually succeeded by 8. patens or Distichlis, and 
commonly these are mixed. The distribution of the areas occupied by these 
smaller grasses will be given in detail in discussing the next higher belt. We 
will simply cite examples here to indicate conditions found at the tension-zone. 
At 1,660 to 1,700 north, for example, S. glabra meets S. patens at the 6.5-foot 
