64 THE RELATION OF PLANTS TO TIDE-LEVELS 
Laboratory. Other tufts of it were found at the same point growing as 
epiphytes on Fucus and Ascophyllum attached to the same log. Bostrychia 
rarely assumes this epiphytic habit in summer, but in fall, winter, and spring 
it is common on the rockweeds, as we shall see when discussing in detail the 
alge of the wharves. 
Delesseria leprieurw is a small, smoky green alga 2 or 3 cm. high, which has 
been found only occasionally. It was first recorded in 1908 as growing on a 
sunken log at the 4-foot level near 250 north by 1,000 east. It was recorded but 
once again (1,750 north by 1,080 east at 1-foot) until September 1911, when 
it was found abundantly on a number of logs along the west shore between 
1,200 and 1,500 north near the 3 or 4 foot levels. This alga, like Bostrychia, 
has not been found among the Spartina stalks, as it apparently was by 
Holden (see Collins, 1905). It is barely posisible that one or both of them 
may occur in this habitat during the fall or spring, but the rather hurried 
searches made for them at these seasons have failed to reveal them. Delesseria 
is perhaps the best example that we have found at Cold Spring Harbor of an 
alga that is transient in character. It occurs in considerable abundance in one 
or more places in any given season and may be wanting in any one of these places 
or even in the whole harbor in other seasons. 
B. THE MID-LITTORAL ROCKWEED ASSOCIATION, ON WHARVES BETWEEN 
1.5 AND 6.5 FEET. 
The part of the mid-littoral belt that we are now to discuss is one showing 
quite definite vertical limits and characterized by a considerable number of 
alge, which are largely restricted to the wharves. There are also certain others 
which, though they may occur sparingly below this belt, or elsewhere within it, 
never reach their fullest vigor or luxuriance except on the walls of the wharves. 
It might be expected that the more natural portions of the harbor boundary 
_would offer the best opportunity for studying the distribution of alge in the 
harbor. As a matter of fact, the walls of the wharves form the only considerable 
area of proper substratum for many of the alge characteristic of this belt. 
These areas are therefore the only ones offering adequate opportunity for the 
study of the vertical distribution of some of the most important species in this 
belt, and of the factors determining this distribution. 
About 20 species of alge have been recorded as occurring on the stones, 
piles, and logs of the docks and wharves, and on parts of wrecks. A few species 
of Calothriz and Lyngbya here mentioned are more abundant just above the 
upper limit of our belt, but are mentioned here only for the sake of brevity. 
These species, arranged in systematic order, are the following: 
Schizophycee: Calothriz (2 species), Lyngbya (2 species), Oscillatoria 
(sp. 1), and Rwularia. 
Chlorophycee: Bryopsis plumosa, Monostroma (sp.?), Rhizoclonium (2 
species), Ulothria flacca, Ulva lactuca. 
Pheophycee: Ascophyllum nodosum, Fucus platycarpus, F. vesiculosus, 
Pylavella littoralts robustus, and Ralfsia clavata. 
Rhodophycese: Bostrychia rivularis, Delesseria leprieuru, Hildenbrandia 
prototypus, and Porphyra laciniata. 
By far the most prominent alge on these wharves are Ascophyllum and the 
two species of Fucus, while Rhizoclonium and Bostrychia come next in abun- 
