ALG OF UPPER LITTORAL BELT 95 
course, an alga growing on the surface must be immersed in salt water from 
1 to 3 hours each tide, except during a few neap tides of each series of neaps. 
But in the 9 to 11 hours in which the Rivularia is exposed, if it takes up any 
water from the soil, to which it is closely attached, it must be fresh or nearly 
fresh water. Another evidently distinct species of Rivularia was found occa- 
sionally between the 7 and 8 foot levels on sunken logs (1,240 north by 575 
west). 
Spirulina tenussima: One of the surprises of the study of the felts on the 
Spit was the discovery of occasional threads of Spirulina scattered among the 
other alge. It is evidently able to persist here when protected by the other 
constituents of the felt, and by the shade of the seed plants, though it does not 
form gelatinous coats, as it does over the Zostera near the low-water level. 
It is evident from the above description of the distribution of these Schizo- 
phycee, as well as from the account given earlier of the growth on the wharves, 
that the 6.5-foot level is not a dividing-line that marks absolutely the upper or 
the lower limit of distribution of certain of these blue-green alge. That is, 
some forms that are equally characteristic of the mid-littoral belt may be rather 
abundant just above the 6.5-foot level, e. g., Anabaena torulosa, Lyngbya 
estuaru, Sprvrulina tenuissima, and Microcoleus chthonoplastes. On the con- 
trary, other species that are characteristic of this upper littoral belt may occur 
in the next lower belt. For example, Calothrix crustacea, Lyngbya semiplena, 
etc., are usually found above the 6.5-foot level, except where unusual local 
conditions have prevented the Spartina glabra from reaching its normal upper 
limit. In such places the Calothrix pushes down the beach to the upper edge 
of the Spartina, even as low as the 6-foot level. 
CHLOROPHYCEA. 
All of the Chlorophycee of this belt, with the possible exception of a species 
of Ulothriz, are forms that are characteristic of the belt below. They manage 
to push up into the present belt, however, in certain especially favorable locali- 
ties where the shade, the character of the soil, or the running water of tide- 
streams or fresh-water rivulets render the bottom constantly wet or damp. 
The species of green alge which have thus far been noted above 6.5 feet are 
the following: 
Cladophora expansa is found somewhat frequently on the west shore of the 
harbor at 7 feet, as a minor component of the looser mats of Lyngbya, Rhizo- 
clonium, Microcoleus, etc. It reaches its higher limit of 7 to 7.3 feet near 
fresh-water inlets, where it forms thin but nearly pure tangles over the soil, 
between the plants of Scirpus robustus (1,670 north by 750 west). A very 
striking characteristic of this Cladophora, as developed at these high levels on 
the beach, is the sparse branching. This has already been referred to in speak- 
ing of this alga in the mid-littoral belt. In many plants the successive lateral 
branches may be separated by 15 or 20 cells of a perfectly simple main axis. 
In April 1911, tufts of Cladophora were abundant in the Inlet, but nothing 
could be seen of these tangles of Cladophora along the upper beach. It is 
probable that some of the filaments of green alge found in the felts above 6.5 
feet on the Spit and Marsh are really threads of Cladophora, but their short- 
ness and the entire absence of branches make it impossible to determine whether 
these are fragments of Cladophora, of Rhizoclonium, or of Chetomorpha. 
T 
