LITHOPHILOUS BENTHOS oo 
the score, in 1909 and 1910 only a dozen or fifteen could be found in the whole 
harbor. Not half a dozen attached plants have been seen in the Inlet or Inner 
Harbor during the past two years. The filling up of the area of the Outer 
Harbor just north of the Inlet, which is correlated in some way with the abun- 
dance of mussels, has driven Grinnellia out of the area where it was formerly 
abundant, and from which the Inner Harbor could be readily supplied with 
spores and drifting plants. It is clear that in this, as in the case of the other 
red alge mentioned, we can not know with certainty the explanation of their 
distribution in the summer until we know more of their distribution and activi- 
ties during the other seasons of the year. 
Polysiphonia is abundant in some seasons on pebbles on the bottom of the 
Inlet from 2,000 to 2,600 north, between mean low water and —3 feet. Tetra- 
sporic plants are common in summer, while cystocarpic and antheridial ones are 
usually rare. In late September 1911 this alga was far more abundant than it 
has ever been in midsummer on the bottom of the east side of the Inlet from 
mean low water downward. In the region between 2,000 and 2,200 north, which 
was most carefully examined at this time, there were often 10 to 15 dense tufts 
to each square meter. All of these plants that were examined proved to be 
sexual, chiefly cystocarpic. In most summers a few drifting plants of Poly- 
siphonia are found in the Inner Harbor, some of them attached to small pebbles. 
In other summers these and the attached plants of the Inlet are practically 
wanting. When, therefore, we find in some succeeding summers a relatively 
large number of these plants in the Inlet, we are inclined to conclude for this 
species, as for the others mentioned above, that the new plants must come from 
spores brought in from the Outer Harbor, rather than from any perennating 
portions of plants of a former summer left in the Inner Harbor. The great 
abundance of this species in September 1911, however, suggests the possibility 
that its basal portions may be constantly present, but that its shoot is well- 
developed only in occasional summers, when conditions are unusually favorable 
at that season. 
The free or drifting plants of the red alge of the Inner Harbor that have 
been noted above may in some species remain in the living condition but a short 
time. Such, e. g., is usually the fate of the Ceramiums, Chondria, Dasya, and 
Polysiphonia. Other species, on the contrary, like the green alge Cladophora 
and Hnteromorpha, may persist indefinitely and even continue to develop. 
Thus, e. g., when Agardhiella, Gracilaria, and Grinnellia lodge on the bottom 
near low-water mark, they may continue to produce tetraspores or cystocarps 
for weeks after being torn loose from their substrata. In this way, of course, 
spores of alge not before growing in the harbor may be dispersed about it in 
considerable numbers. 
C. EPIPHYTIC ALGA ON ZOSTERA AND ULVA. 
About 7 or 8 species of the alge of the Inner Harbor are attached to other 
plants, chiefly to Zostera. In fact, it is the presence of Zostera, to serve as a 
substratum, that alone makes it possible for most of the epiphytic species to 
grow at all abundantly in the Inner Harbor. It is because of this importance 
of Zostera as a substratum that we have indicated its distribution on our topo- 
graphic map of the harbor. 
3 
