ROCKWEED ASSOCIATION fO3 
not grow on the faces of these planks above 6.25 or 6.5 feet. On the east wall 
of the wharf of the Research Laboratory, also at 1,100 north, the upper limit of 
Fucus is at 6.5 feet where exposed to the sun for the whole morning, but it goes 
up to 7 or even to 7.25 feet in the shade on the north sides of piles where 
protected from the sun and desiccation. 
Fucus is prevented from occupying the very base of the walls of the wharf 
by the mud which would bury it, and perhaps also by the greater turbidity of 
the water at this lower stratum. /wucus, in general, is much less abundant in 
the lower third of the rockweed belt than in the upper two-thirds. It seems 
even less able than Ascophyllum to endure prolonged immersion in fresh water, 
as is shown by its distribution in relation to the fresh-water streams entering 
the harbor along the shore, or through the walls of the wharves. The only 
efficient competitor of Fucus on the wharf is Ascophyllum, which may shade out 
the Fucus or tear it off by the aid of a greater weight and toughness. 
Interesting facts concerning the seasonal development of Mucus were sug- 
gested by its condition in April 1911. At this time the upper border of the 
band of Fucus was marked by a series of sporelings 1 to 3 cm. high, which were 
of a reddish-brown color, unlike the usual brown of Fucus, and shriveled up as 
if killed by frost. The Fucus plants on long stretches of the wall showed at 
this season not a single well-developed receptacle, where in summer dozens could 
be found. On some parts of this wall a few plants were seen with receptacles, 
but these were immature. It is evident from what is recorded above, of the 
condition of Ascophyllum in April, that the fruiting season of the latter is 
inaugurated much earlier than that of Mucus. Observations prolonged over 
the late fall and winter are needed to determine exactly the duration of these 
fruiting seasons. 
Pyluella littoralis robustus: This alga has been found in abundance on the 
wharves, only in April 1911. Its habitat was then the wharves of the west 
shore, especially the wharf of the Research Laboratory, between 2 and 3.5 feet. 
Several times during the summer it has been found in small tufts, always on 
the Research Laboratory wharf in shaded spots between the 3 and 4 foot levels, 
usually on the north end of the wharf, and more rarely in the shadow of piles on 
the east side. This alga has nearly always been found in summer in the Creek 
near 200 south. It is evidently favored by the low temperature of the water 
here, and by the protection from desiccation at low water. 
Ralfsia clavata (Carm.) Crouan: This light or dark brown incrusting alga 
occurs on the piles and stones of wharves, especially of the west side of the 
harbor. It forms small, smooth, adherent disks each from 1 or 2 to 12 or 15 
mm. in diameter, which, when old, have a slightly wavy outline. They are at 
first thin and tightly adherent but later become thick and more easily detached. 
This form is found in summer between the 2.5 and 5 foot levels, chiefly on the 
shaded sides of piles among young plants of Fucus, along the east and north 
faces of the wharf of the Research Laboratory. In April 1911, this species was 
far more abundant at one point than it has ever been in summer. Scores of 
young colonies 2 or 10 mm. in diameter were found on stakes near the wharf 
at 400 north by 170 west at 2.5 to 4 feet. The few observations made elsewhere 
in the harbor in April showed no unusual abundance of the alga, at this season, 
in any other location. Ralfsia is not found where subjected to flooding by fresh 
