ALG OF MID-LITTORAL MARSH 5 
is commonly sparsely branched, often simple for 15 or 20 cells. (The cells are 
30 to 45u wide by 200 to 600u long. It is often found mixed with Enteromorpha 
clathrata, Rhizoclonwum, Vaucheria, or various blue-green alge, but it may 
also develop nearly pure growths, forming loose fluffy tufts on mud about 
the steps of Spartina glabra (e. g., 2,000 north by 825 west). In the neighbor- 
hood of fresh-water rivulets this Cladophora keeps up 10 or 15 cm. above the 
level of the water during low tide. It evidently does not stand well a con- 
stant immersion in fresh water, though it must of course often be washed 
with rain-water during low tide. On April 8, 1911, no tufts of this alga were 
found along the shore. However, tangles of this same Cladophora were present 
in the Inlet on this date in great numbers. It seems certain that spores from 
these tufts must reach the shore, but find the conditions there less favorable 
than in the summer. This is probably because of the absence, in April, of the 
Spartina to give shade, to prevent desiccation, and also to hold the tangled 
threads of the alga. 
Of the two species of Hnteromorpha found in this zone HL. clathrata is the 
most generally distributed. We have already noted that dense tangles, many 
yards in extent, may float up from among the Zostera and drift ashore to settle 
on the Spartina, crushing it down by their weight. Parts of the masses of 
Enteromorpha that sink in shaded places between the clumps of the Spartina 
may persist in a living condition for days or weeks. Far more important are the 
widespread smaller mats or tangles of H. clathrata covering the mud at the 
base of the Spartina stalks, either as pure growths or mixed with several other 
green or blue-green alge. The H. clathrata of these mats adheres rather firmly 
to the mud, apparently by the silting in of its older parts. It has shorter 
branches and a smaller diameter than the tufted plants found on the Zostera. 
Streaming tufts, like those on the Zostera, are occasionally found in the 
present belt, in tide-pools (e. g., at 0 south by 1,110 east at 3 feet and 
at 0 south by 1,165 east at the 4.5-foot level). In streams where the water 
is quite fresh for a considerable time at each low tide the H. clathrata is 
absent. It is found, however, at higher levels on the banks of such streams, 
out of reach of the fresh water (460 south by 680 east). In April 1911 this 
Enteromorpha was found on the stubble of the Spartina, but not nearly as 
abundant as it usually is in July and was in September 1911. 
Enteromorpha crinita has been found between the 3 and 5 foot levels asso- 
ciated with H. clathrata and with Rhizoclonium, e. g., on the eastern banks of 
the Creek at 200 south (see p. 59). 
Enteromorpha intestinalis, the third species of this genus found in the harbor, 
is characteristic of just those habitats within this belt which are flooded with 
fresh water for from 5 to 10 hours at each low tide. In fact, this species is 
almost entirely confined to parts of the shore near fresh-water streams. Only 
a few smaller plants have been found elsewhere, as, for example, along the 
wharves, on stakes or buoys in the middle of the harbor, or in the channel to the 
Outer Harbor. The largest plants seen were those on pebbles in the tide-pools 
of the side-channel near 50 south by 590 east from 1.5-foot to the 2.5-foot 
levels. The water standing or running over these plants at low tide is but a 
decimeter or two in depth and is nearly or quite fresh. Under these conditions 
E. intestinalis reaches a diameter of 3 or 4 cm. and a length of 5 or 6 dm. In 
the Creek itself #. intestinalis is found scattered sparsely as far up as 450 south 
