SPARTINA GLABRA ASSOCIATION 45 
level, and with very little intermingling the S. patens becomes as completely 
dominant a meter or two above (%. ¢., inshore from) the meeting-line as 8S. 
glabra is a meter or two below the line. Mixed with the S. patens, a little 
higher up are scattered plants of Distichlis, and, in the wetter portions, of 
Scirpus americanus. A few dwarfed, scattered shoots of S. glabra are found 
even as far up as 7 or 7.5 feet. On the well-drained areas the tension-zone 
between the Spartina glabra and the S. patens is much narrower and the last 
scattered stalks of the S. glabra get very little above the 6.5-foot level (e. g., 
at 840 to 900 north). It seems clear that elevation of the soil is the condition 
favoring the success of S. patens in the competition. Thus, for example, at 
1,760 north there is a complete island of S. patens on soil at 7.25 to 7.5 feet, 
surrounded entirely by 8. glabra on soil running up to about the 7-foot level, 
the zone of the latter on the upshore side being 1.5 meters wide. The elevation 
of this patch of soil above its immediate surroundings on all sides, with the 
better drainage thus allowed, was the only discoverable cause of the difference 
in its vegetation. : 
On parts of the west shore where fresh water is abundant 8. glabra encoun- 
ters Scirpus americanus at its upper margin. It is in these areas that we find 
the most interesting and diverse behavior of the salt reed-grass and its com- 
petitor. Hach is dependent upon the character of the soil, its fresh-water 
content, and the amount of shade to which it is subjected. In general, these 
two species, when growing on wet shores, mingle much more freely and widely 
than do 8. glabra and S. patens. For example, at 1,220 north S. glabra 
nearly 2 meters tall becomes mixed with Scirpus americanus at the 6-foot 
level, and then continues on upward to the 7.25-foot level. The Scirpus 
occurs here on soil between the 6 and 8 foot levels that is more or less covered 
by fresh water at low tide, while the Spartina is found as usual on soil above 
the level of running fresh water. At other points nearby (1,325 north), where 
the fresh water, though evidently present in the soil at higher levels, does not 
break out as a rivulet till the 5 or 4 foot level is reached, Scirpus gets down to 
the 5-foot level on higher lumps of peat. In this area the Spartina ceases at the 
— 6.25-foot level, with plants of 6 or 7 dm. in height. At 1,700 north the 
Spartina meets the Scirpus at 6.5 feet, where the latter immediately becomes 
dominant and continues up to the 8-foot level, with only the barest sprinkling 
of dwarfed Spartina plants between 6.5 and 7 feet. In general, then, where 
fresh water is present on an unshaded shore, the Spartina glabra becomes mixed 
with Scwrpus americanus from 6 feet upward. In regions that are both wet 
and moderately shaded we have a very interesting change in the relative 
distribution of these two species. Under these conditions the Scirpus is mixed 
abundantly with the Spartina from 6 to 6.5 or 7 feet and then ceases, while 
the Spartina becomes more abundant again and continues upward in moderate 
shade to 7.5 or even to 8 feet (¢. g:, at 740 north and near 1,350 and 1,400 north). 
The relation of the two plants at these points seems to show that the Scirpus 
americanus cannot endure much shade; that Spartina glabra can endure moder- 
ate shade, as indeed it must when submerged; that Spartina pushes up the 
beach far beyond its competitor Scirpus in shaded areas where fresh water is 
present, and where, therefore, the moisture content of the air about the leaves 
is sufficient to prevent a too rapid transpiration. 
