ROCKWEED ASSOCIATION 69 
PHAOPHYCER. 
We have already seen that two brown algew, the rockweeds Ascophyllum and 
Fucus, give character to the mid-littoral belt on the wharves. We will now, in 
somewhat more detail, take up the distribution of these and the other Phxo- 
phycee occurring on the wharves. (See also plate rx.) 
Ascophyllum: Plants of this alga of all lengths from 1 or 2 cm. up to 0.5 
meter or more are found in the harbor at all seasons. In July or August fertile 
branches or receptacles are infrequent on plants of the Inner Harbor, and 
mature ones have not been seen. In April 1911, plants with fertile clubs were 
numerous and these receptacles bore an abundance of ripe antheridia and 
oogonia. At this early spring season the receptacles were often covered by a 
turf of Ulothrix flacca. In some places Ascophyllum may form nearly pure 
patches between 3 and 5.5 or 6 feet, with 20 or more plants per square foot (plate 
xvil). In other areas it may be mingled more or less equally with Fucus, the 
two together covering the wall of the wharf. In still other places there may be 
considerable gaps in the rockweed belt oftenest filled with Bostrychia or Rhizo- 
clonvum. The rockweeds are probably ground off from these spots by boats and 
ice, and the clean surface so formed is then occupied at once by those algae whose 
spores happen to be ready for attachment and germination at just that time. 
There seems to be no difference in the capacity of Fucus and Ascophyllum to 
grow upon a given substratum within the range of the Ascophyllum. There 
seems also to be some competition between the two, arising from the shading out 
of young plants of the one by older ones of the other. Then too the plants of 
Ascophyllum, being larger, may finally overgrow and shade out even older plants 
of Fucus. It is pretty certain also that the heavier Ascophyllum often tangles 
with the F’ucus and finally tears it loose. 
The substrata upon which Ascophyllum occurs include wood, shells, sand- 
stone, some kinds of granite, and gneiss. On the wharves of the east side, 
however, it was noted that certain large yellow granite stones, between 1,000 
and 1,600 north, contrasted strongly with the dark sandstone, gneiss, and 
schist of the rest of the wall, in being entirely bare of Ascophyllum and Fucus, 
even where the immediately adjoining stones of the wall above, at the sides, and 
below, were densely covered with these rockweeds (plate 1118). ‘The general 
chemical character of the barren blocks of granite, we are told by a competent 
petrographer, is essentially like that of the well-covered blocks of gneiss and 
darker granite. Moreover, the physical character of the barren stones does not 
seem sufficiently unlike that of the covered ones to explain the barrenness of the 
former. 
Ascophyllum grows only in salt or brackish water, but it is capable also of 
enduring wetting by splashing fresh water or even by submergence of parts of 
the plant in fresh water for 2 or 3 hours of each tide. We have mentioned above 
(p. 61) its occurrence near the outlet of the artesian wells at 1,435 north on 
the east side. Perhaps different branches of each plant may be immersed in suc- 
cessive low tides. In another habitat on the east side, namely, the fresh-water 
pool just south of the mill, Ascophyllum does not grow below 5 feet, the level 
of the fresh water at low tide, but it does grow just above this where exposed to 
the air or even to a spray of fresh water for 7 or 8 hours each tide. At 1,010 
north on the east shore the rocks of the wharf washed by fresh water from the 
entering stream are bare of Ascophyllum. Asa last example, plants of this alga 
