46 THE RELATION OF PLANTS TO TIDE-LEVELS 
The other angiosperms which may mingle with Spartina glabra along its 
upper margin on the west shore are, in order of abundance, Solidago semper- 
virens, Atriplex patula, and Scirpus robustus. Of these, Solidago and Atriplex 
occasionally mingle with Spartina glabra near the 6.5-foot level (e. g., 1,250 
north), but they are usually encountered by the Spartina only when it has 
pushed farther up the beach. This is true also of Scirpus. None of them 
except Scirpus robustus (at one or two spots) is an important competitor of 
Spartina, and further discussion of their distribution may be left until we 
take up that of the plants of the next higher belt. 
The mid-littoral Spartina belt on the Marsh at the head or south end of the 
harbor is more largely developed than on any other part of the shore except on 
the eastern half of the Spit. Aside from the greater variety of competitors met 
at some points along its upper margin the general character of this broad belt 
of Spartina glabra is similar to that on the Spit. 
Since a special study has been made of the successive levels of the whole 
Marsh at the head of the harbor (mid-littoral, upper littoral, and supra-littora] 
marshes), and Professor Conard has mapped in detail the vegetation of a 
selected strip, cutting across all three of these belts (see plates x1, xxI, and 
XXII), we will here only sketch the most general features of this portion of the 
mid-littoral belt. It will be noticed at once on plate x1 that the main stream 
cuts into halves the whole marshy area south of the harbor, from the 1.5-foot 
level up to the 9-foot level. The portion on the west of the stream is chiefly 
below the 6.5-foot level and therefore largely occupied by Spartina glabra. 
. That east of the stream lies chiefly above the 6.5-foot level and therefore has 
a relatively narrow belt of Spartina at the north and a bare fringe along the 
stream. The lower limit of the Spartina across the whole northern border of 
this belt, from 200 east to 1,000 east, is between the 1.5-foot and 2-foot levels, 
a little higher on the average than on the east end of the Spit and than on the 
-Mmore open portions of the east and west shores of the harbor. The stand on 
the south shore is rather thinner at the edge, but soon attains a density com- 
parable with that on the Spit, and increases also in size as it goes up to higher 
bottom (indicated in the section of soil and vegetation, figure 3). On each side 
of the large stream, a shoal, coming just above the 1.5-foot level, begins at 50 
north and stretches northward toward the harbor. The shoal on the west side 
is being steadily taken possession of by Spartina glabra, which, during the six 
years our investigations have covered, has advanced several meters. Comparison 
of the present northern limit of the Spartina in this locality with that shown on 
a map made in 1902, by Shreve, indicates that it has pushed northward 12 
meters in 10 years. The shoal at the east of the stream is not being occupied 
by the Spartina, probably because the corner of the Spartina belt at 75 north by 
650 east is held back by an artificial bathing-beach across the south end of the- 
shoal, which is cleaned off each year. The irregularities in outline of the 
Spartina belt west of the stream, especially in the deep notch at 400 east, are 
apparently connected with the entrance of a stream that is dry in summer but. 
in winter and spring carries considerable fresh water into the harbor. 
Along the Creek and the tide-stream at 1,000 east the character of the lower 
margin of the Spartina belt differs on different parts of the stream-bank. 
Having incidentally referred to the conditions along the tide-stream when dis- 
cussing the Spartina of the east shore, we will here discuss conditions only along- 
