1916] CURRENT LITERATURE 79 
This body of water is separated from the larger outer harbor by a spit of 
sand and gravel. The shallowness of its water may be noted from the fact 
that its area of 110 acres at mean high tide is reduced to 45.5 acres with the 
8-foot recession of the waters at mean low tide, while a further drop of 1 foot 
effects a further reduction to only 17 acres. The various levels were carefully 
marked by a large series of stakes set along the contour lines. In this way, 
using mean low water as zero, four vegetational belts were delimited: (1) the 
region of bottom vegetation from —3 to 1.5 feet, occupied by an algal associa- 
tion composed of Ulva and Enteromorpha together with an association of seed 
plants consisting of Zostera marina and Ruppia maritima, rooted in the muddy 
bottom; (2) the mid-littoral belt, from 1.5 to 6.5 feet, with the Spartina 
glabra marsh and the algal rockweed associations, the latter being dominated 
by Fucus and Ascophyllum; (3) the upper littoral belt, from 6.5 to 8 feet, 
with associations dominated by species of Spartina, Juncus, and Scirpus; and 
(4) the supra-littoral belt, from 8 to 12 feet, containing many species combined 
in intermingling associations. 
In the careful analysis of many of the factors influencing the distribution 
of littoral plants, the substratum is found to consist of the lower stretches of a 
valley in glacial gravel and sand. The upper part of the valley is occupied by 
a small stream of fresh water flowing into the harbor, while in the harbor 
itself there is superimposed upon the gravel a black mud of varying depth, 
passing upward into a muddy peat formed by the remains of the salt marsh 
vegetation. The deposition of this peat is of such a character as to indicate 
comparatively recent coastal subsidence estimated at a minimum of 6 feet. 
Boulders of considerable size and the walls of wharves largely determine the hori- 
zontal limits of the rockweed association, while the larger plants act as the sub- 
stratum for a varied epiphytic vegetation comprising most of the red algae; 
the abundant mussels are seen to be important in anchoring Ulva and Entero- 
morpha clathrata. Details of the interaction of the plant life and these sub- 
Strata are rather carefully worked out. 
Water currents due to tidal movements through the narrow channel at 
the end of the spit and to the inflowing stream of fresh water seem to be im- 
portant in effecting distribution of the species, both through the transporta- 
tion of the plants themselves, either broken or entire, and by the dispersal 
of seeds and spores. A secondary effect of currents is shown to be in 
changing the concentration of solutes about the plants themselves. Aeration 
is suggested as one of the important results, and further data are promised 
as to the distribution and effects of salinity. Tidal movements as effecting 
changes in water are the factor, or rather the complex of factors, given most 
attention, and an analysis is made of the character of the tides as related to 
(1) submergence and exposure, (2) evaporation, (3) aeration, (4) salinity of 
soil water, (5) effect on exposure to rain, and (6) effect on light supply. ape! 
data are tabulated regarding the duration of submergence and exposure, and 
the ratio between the duration of the two is determined. The Sisixibdions 
