SEED PLANTS OF UPPER LITTORAL BELT 85 
distributed (plates xt and x11). There are but four patches of it on the west 
side and only six on the Marsh, and it is entirely wanting from the east side, 
north of the Marsh, and from the Spit. This species of Scirpus is, in fact, less 
abundant and less widely distributed than several of the other plants of this belt 
to be mentioned later. It is discussed here, immediately after S. americanus, 
for the sake of more ready comparison with this species. S. robustus is con- 
fined, like its relative, to areas with fresh soil-water. It rarely forms pure stands 
of any considerable extent. Stands of 50 square meters are found at 1,600 north 
on the west side, and one near 500 south by 880 east. Nearly pure stands of 
smaller area are present at 590 south by 740 east and near 120 south by 1,200 
east. More often it is mingled with Spartina glabra, S. patens, or Scirpus 
americanus; e. g., on the west shore at 1,980 to 2,020 north or on the Marsh at 
550 south by 730 east. The lowest level from which this species has been 
recorded is 7 feet and its upper limit is at 9 or 9.25 feet. As was suggested 
above, this Scirpus is found only on soils supplied with fresh water. In some 
areas this water is evident on the surface, e. g., on the west side at 1,415 north, 
on the Marsh at 120 south by 1,200 east. In other places the fresh water is not 
at first evident, but is found on investigation to be present in the soil. A striking 
instance of the latter sort is the small area, between two streams at 470 south by 
830 east, which is elevated 1.5 or 2 feet above the bed of these streams. ‘his 
area is covered with a mixture of Spartina glabra, 8. patens, Scirpus americanus, 
and, most prominent of all, the present species. ‘This same mixture extends 
eastward from the point named on soil, from 8 or 10 inches below the surface, 
of which a rivulet of fresh water trickles out at low tide. Not only is the soil- 
water fresh, but the overlying water at high tide never becomes very salt. Spe- 
cific-gravity tests made at this point when the tide was at the 8-foot level showed 
a density of but 1.005 at the surface of the soil bearing these plants. At the 
time of the spring tides, which in summer reach 9 feet, or of storm tides, which 
in summer reach 10 feet and in winter even 12 feet, all inflowing fresh water 
must be backed up south of the road embankment, which crosses the Creek. The 
whole Marsh would then be covered with from 1 to 3 feet of sea-water with a 
density of 1.019, like that of the harbor itself. This shows that the shoots and 
more superficial roots and rhizomes of this plant can endure submergence in salt 
water for several hours a day, even when in a growing condition. It is probable, 
however, that the salt water never penetrates far into the soil here, because of 
its compactness and of the constant supply of fresh water from below. 
Distichlis spicata on the upper littoral belt: This is a slender grass 4 or 5 
dim. in height, with narrow, often glaucous leaves. It grows, chiefly between the 
6.5 and %.5 foot tide-lines, in a number of small areas on the Spit, at a few 
points on the Marsh, at one point on the east side, and two on the west shore 
(plates v, x1, and x1v). Pure, or nearly pure, stands of Distichlis are found 
at a few points on the Spit (plate xx B). These are but a few meters long each, 
but 6 or 8 dm. wide, and all are near the 7-foot tide level (e. g., 500 east at 7.75 
feet, 580 to 590 east at 6.5 to 7.5 feet, and 800 to 820 east at 6.5 to 7.5 feet). 
On the Marsh similar dense growths of Distichlis, over smaller areas, are found 
at 0 north by 940 east at the 7.25-foot level, and at 370 south by 820 east near 
”.5 feet. Elsewhere about the harbor Distichlis is mingled with Spartina 
patens, as at several points on the Spit (950 east, 800 to 1,000 west), on the 
