ALG OF MID-LITTORAL MARSH 61 
400 and 600 east at the 6.5 to the 7.5-foot levels. There is possibly also some 
subterranean fresh water in the soil of this area, for it comes out in rivulets 
just south of this. 
PH EOPHYCER. 
The most prominent brown alge of the mid-littoral marsh are Ascophyllum 
and Fucus. ‘These are the same species that dominate the same levels (1.5 to 
6.5 feet) on the walls of the wharves. On this marshy belt, however, these 
algze nowhere form a pure stand over any considerable area, since there are 
no extensive stony beaches to give them a satisfactory footing. Only on the 
east side of the Inlet and on an occasional log, stone, or shell about the other 
shores of the harbor do these alge find, between these levels, a satisfactory sub- 
stratum for attachment. (For distribution see plate rx.) 
Ascophyllum nodosum is scattered about the whole circumference of the 
harbor, and throughout the entire width of the present belt. At the lower levels 
it has much the same size and coarseness as on the wharves. At the upper levels, 
especially in places exposed to high temperatures, this alga remains smaller and 
the branches are much more slender than those of the plants growing on the 
wharves. On the shore, as on the wharves, ripe receptacles are rare during the 
summer, though abundant during the spring. The distribution of Ascophyllum 
in relation to fresh water is seen best along the natural shore. By the main 
stream, from 10 north to 600 east, ete., Ascophyllum grows 2 feet long and is 
fertile, but it keeps just above the level of the fresh-water stream at low water. 
Again, at 1,000 north on the east shore, there is a vertical strip of stone wall 
3 feet wide, horizontally, that is bare of Ascophyllum, where a fresh-water 
stream runs through the wall. In the pool of fresh water just south of the mill, 
Ascophyllum is found on logs and stones about the border, but always just above 
the level of the surface of the pool at low water, which is at 5 feet. Only at two 
spots along the eastern side of the harbor (1,435 north and 2,050 north), where 
the water from artesian wells flows over or between the pebbles of the bottom, 
does Ascophyllum seem to grow where it is wetted with running or splashing 
fresh water at low tide. Closer examination of the plants near the outflow from 
these wells shows that only part of the thallus is actually submerged in the fresh 
water during any one low tide. The other branches are held above the water by 
the submerged ones and by those stones and pebbles between which the water is 
flowing, as they would not be in the more definite channels of the streams along 
the natural shore of the harbor. In the spray-zone also not all parts of the sur- 
face of a plant are completely flooded all the time. On the whole, it seems 
evident that these plants of Ascophyllum, in common with those of the wharves 
and shore, are really enabled to carry on some gaseous exchange with the air 
during low tide. It must, of course, be remembered also that in the turbid water 
of the Inner Harbor the light supply of even slightly submerged plants would 
be greatly diminished. The exclusion of light would probably be just as efficient 
a cause in keeping Ascophyllum above low-water level as would be the cutting 
off of the more ready access to CO,. We may note also that while the lower limit, 
in the Inner Harbor, of Ascophyllum and its associate Fucus is about 1 to 1.5 
feet above mean low water, they occur at 1 or 1.5 feet below mean low water on 
the rocky beaches of Long Island Sound. In this latter habitat the water is 
much clearer and so would allow more light to reach plants that are continuously 
submerged, as some of these plants of Ascophyllum and Fucus must be for 
