OZ. THE RELATION OF PLANTS TO TIDE-LEVELS 
several tides in succession, during each series of neap tides. But the water of 
these open shores is also much better aerated by the constant movement, and 
thus may furnish a much better supply of the necessary oxygen and CO, to a 
submerged plant than it could obtain from the water of the Inner Harbor. It is 
also true that the paraphyses of /ucus, for example, are much better developed 
on plants in the Sound, which may perhaps aid in the absorption of CO, from 
the water. Nowhere in the neighboring parts of the Sound have Ascophyllum 
or Fucus been found at more than 2 or 3 feet below mean low water. The same 
inability of these plants to withstand constant submergence is indicated by their 
absence from tide-pools. This has been noted in the cold water of Casco Bay, 
Maine, as well as at Cold Spring Harbor. 
It seems clear that the absence of Ascophyllum or Fucus below the 1-foot 
level in the Inner Harbor may be due either to the insufficient light or the 
insufficient opportunity of gaseous interchange. Only a carefully planned study 
of the problem can show definitely just how far each of these factors is concerned 
in determining this lower limit. 
Two species of Fucus (Ff. evanescens and F. vesiculosus) are distributed 
about the harbor in this mid-littoral belt. These are found along with the 
Ascophyllum wherever a stone, a sunken log, or a shell, including the shells of 
living mussels, gives them a footing. J’. evanescens occurs rather rarely on 
large stones in open places. 
Fucus vesiculosus is far more abundant and widely distributed, and is repre- 
sented by at least three distinct varieties. The typical form of the species, the 
robust one characteristic of the vertical walls of the wharves, occurs also on 
stones of the bottom. These latter are chiefly stones that have fallen from the 
wharves, and are especially abundant along the east side of the harbor. But 
this robust Fucus is also found on larger pebbles and stones in the lower parts 
of this belt far from the wharves, for example, in the Inlet or less frequently 
_ along the west shore from 600 to 2,200 north. The distribution of I’. evanescens 
and of the typical F’. vesiculosus is in general similar to that of Ascophyllum, 
except that they may grow at somewhat higher levels. Their distribution is 
apparently determined by the same factors that affect Ascophyllum. 
The variety of FP. vesiculosus which is most widely distributed on the marshy 
shore is a more slender form (probably F. vesiculosus laterifructus Grev.). 
This variety grows in habitats between the 1.5 and 6 foot levels that are more or 
less shaded by Spartina glabra. The fronds of this Fucus are attached either to 
pebbles or shells, and never, so far as seen, to the stalks of the Spartina. 
Nowhere does this variety become as dwarfed and attenuated as it does on the 
muddy shores of certain more protected near-by harbors, such as Lloyd’s 
Harbor. In this variety of Fucus we have another excellent opportunity for 
an experimental study of the factors determining a particular type of plant 
structure. (Plate xv1B.) 
Perhaps the most interesting variety of Fucus found about the harbor is F. 
vesiculosus var. spiralis (.) Ag. (plate xv1A). This form occurs between the 
1.5 and 6 foot levels, chiefly along the west and north shores of the harbor. It 
is sparse in the fringing Marsh at 50 to 150 north by 700 to 1,000 east and is 
most abundant in the large Spartina area south of the east end of the Sandspit, 
where scores of plants occur tangled together in a single square meter. This 
variety differs from all the other forms of Fucus mentioned in habit, since it is 
