74 THE RELATION OF PLANTS TO TIDE-LEVELS 
practically pure growth of a single one of these species, as is most often true 
of the grasses or Juncus. In other places the shore may be occupied by an asso- 
ciation made up of two or three of these species. In a few regions the upper 
littoral beach is either entirely bare, in which case it may be either pebbly, sandy, 
or muddy in character, or it may bear close, blackish felts of minute alge. The 
latter are most often found on the more stable, pebbly bottoms. 
The eight species which, over larger or smaller areas, determine the character 
of the vegetation in this belt, are the following; they are mentioned in the 
order of their general prevalence: Spartina patens, Sueda maritima, Sali- 
cornia europea, Juncus Gerardi, Scirpus americanus, S. robustus, Distichlis 
spicata, and Salicornia ambigua. Only nine other species have been recorded for 
this belt. Six of these nine species that may be nearly pure over small areas, or 
may be scattered among other species just above the Spartina glabra belt, are 
these: Atriplex patula, Limonium carolinianum, Plantago decipiens, Scirpus 
nanus, and Triglochin marituma. The other three species of seed plants that 
have occasionally been seen in this belt are Atriplex arenaria, Iris versicolor, 
and Samolus floribundus. Of these, the latter two are to be regarded as inwan- 
derers, on wet shores, from the next higher belt. Their distribution is indicated 
in the list of plants and plant habitats at the end of this paper. 
Each of the eight dominant species, except Scirpus, is distributed rather 
generally about the harbor, but the Salicornias and Sueda are represented by 
relatively few and scattered plants except on the Spit, while Juncus gerardi is 
nearly absent there, though abundant on the Marsh. Scirpus americanus and 
S. robustus occur only where fresh water is present on the upper littoral beach. 
These species are therefore entirely absent from the Spit. It is only rarely 
about this harbor that Juncus gerard directly succeeds the Spartina glabra, as, 
e. g., at 200 south by 1,150 east or at 550 south by 890 east. Juncus is usually 
separated from the Spartina glabra by a band of S. patens. 
We may now discuss, in some detail, the general distribution and interrela- 
tions of the eight dominant species, and then attempt to discover the factors 
determining their distribution. Our treatment of those species occurring on the 
Marsh will be relatively brief, since this area has been closely studied and 
mapped in detail (plates x1, XxI, and XXII). 
Spartina patens: This species, as was suggested in discussing the next lower 
belt, is most abundant on the estuarial marsh at the south end of the harbor, 
though present elsewhere, on parts of the upper littoral belt which have a gentle 
slope, and no fresh water flowing over them. 'The need of these conditions 
limit the development of a continuous zone of this plant chiefly to the northern 
and western portions of the Marsh, and to the western fourth of the south shore 
of the Spit. Elsewhere this grass occurs in narrow and short strips, chiefly 
between the 6.5 and 7.5-foot levels. We may illustrate the first type of area by 
describing in a general way the growth of Spartina patens on the Marsh and on 
the west end of the Spit; then we may note briefly the distribution of the narrow 
strips about the whole shore. 
Spartina patens on the Marsh: This grass, growing in dense turfs, dominates 
nearly half the area of the estuarial marsh, east of the Creek, above the Spartina 
glabra. This area lies chiefly between the 6.5 and 8 foot levels, but at certain 
points on the Marsh this grass may get d~.,n as low as 5.5 feet (200 north by 
1,020 east), while at other points it may run up nearly to the 9-foot level (100 
