80 THE RELATION OF PLANTS TO TIDE-LEVELS 
at the 6.5-foot and in a few cases at the 6-foot level shows that it can withstand 
a submergence of 3 to 3.5 hours per tide, or 6 or 7 hours per day. Its occurrence 
at the 7.5 foot and, more rarely even at the 8.25-foot level, where the shoot may 
not be submerged for several days together, shows likewise that frequent sub- 
mergence of the shoot is not necessary, even in regions with a rather dry atmos- 
phere, like the Spit. The plants of Sueda are, however, rarely so high on the 
beach that their roots can not reach to a soil that at least part of the time is 
saturated with salt water. It is to be recalled here that, as one can see on any 
calm day on the beach, the tide-water is carried up several inches above high-tide 
level by capillarity. This means that the water goes considerably higher in the 
soil than the 7 or 7.5-foot level at high water of a neap tide. That this level of 
the soil-water is a factor of some importance to the Suceda is indicated by the 
fact that, e. g., at 800 to 900 east on the Spit, this species stops near the 8-foot 
line, leaving a beach above this that is quite bare of vegetation. In this place 
there are no discoverable differences in the soil above and below the 8-foot level, 
and there are no plant competitors above this contour. It seems probable, there- 
fore, that the lack of sufficient soil-water may be the condition excluding Sueda 
from the upper levels of this shore. Unfortunately no actual determinations of 
the water-level or of the salt-content of the soil-water have as yet been made at 
this point. 
On some parts of the upper littoral beach, as has been noted above, the Sueda 
is displaced from levels between 6.5 and 7.5 feet by Distichlis or Salicornia 
europea. Whether the competition between these plants is such that some 
slight local difference in the character of the soil may give one or the other of 
these two species the advantage over the Sueda is uncertain. It is possible that 
the greater amount of humus usually present in the soils occupied by these 
two competitors may allow them to become established in these areas, while in 
the more purely sandy soil Sueda is the successful competitor. 
Salicornia europea in the upper littoral belt: This plant is found abun- 
dantly on the Spit, often in dense stands for from 5 to 20 meters along the shore. 
It is widely but sparsely scattered over certain parts of the Marsh also, while 
it is wanting from the other two sides of the harbor, except for two points on the 
eastern shore. (See plates v, XA, XIII, and XIV.) 
On the south shore of the Spit this species of Salicorma reaches its maximum 
development in size and abundance as well as in purity and density of stand. 
At the western end of the Spit (980 to 1,000 west), this Salicornia was found 
scattered thickly through a belt of dwarfish Spartina glabra some 4 or 5 meters 
wide, near the upper border of the latter. Near the 7-foot level Salicornia is 
mingled with Spartina patens, also with some Distichlis and Sueda, while at 
the 7.5-foot level Salicornia becomes completely dominant. Farther eastward 
the sprinkling of Salicornia becomes more copious, e. g., though this upper 
littoral belt from 480 to 590 west was dominated by Sueda, there was an admix- 
ture of nearly as many plants of the Salicornia. Between 380 and 480 west 
this belt is dominated by Salicornia europea, except for an occasional narrow 
bar of Spartina patens cutting across it. Between 200 and 380 west this — 
Salicornia is usually very sparsely represented, but from 200 west to 20 east it 
is, in most years, exceeded in numbers only by Sweda. Eastward from the latter 
point Salicornia dominates this upper littoral beach as far as 280 east, though 
often mixed with abundant Sueda. Next follows a stretch dominated by 
