ALG OF MID-LITTORAL MARSH oF 
grow inland far from the sea, suggested the possibility that the present species 
might persist indefinitely in fresh water. Miss Stella G. Streeter, in the summer 
of 1910, attempted to determine this experimentally by moving pebbles bearing 
E. intestinalis to a point in the same stream above the reach of the tide. This 
resulted in the death of all plants thus subjected to a constant immersion in 
fresh water, in 16 or 18 days. Similar experiments with Monostroma, which 
is likewise associated with fresh water, showed that it is even less resistant to 
constant submergence in fresh water. The reason for the association of 
Enteromorpha intestinalis with fresh water has not been determined. It is 
conceivable that it may be because the Hnteromorpha finds these habitats 
endurable for it and at the same time free from many competitors which it 
would encounter in really salt water. The fact that H. intestinalis grows in 
tide-streams, or on open shores, suggests also that the movement of the water 
in fresh-water streams may make these favorable habits. 
Some observations were made on the rate of growth of sporelings of this 
species of Hnteromorpha and of H. clathrata. Blocks of wood and stones placed 
beside H. intestinalis in its native habitat showed a crop of young plants from 1 
to 2 mm. high in 3 weeks’ time. Logs of a floating raft placed in the water on 
July 15 had many plants of H. clathrata on them by August 15, and they were 
8 to 10 cm. long. The rate of growth in length of mature plants of H. intesti- 
nalis was also measured by Miss Streeter. In plants averaging 60 mm. in 
length at the start Miss Streeter found an average daily increase, during 20 
days of observation, of 2.5mm. The maximum daily increase observed was about 
4mm. Unfortunately these plants, even when left undisturbed in their native 
tide-pools, do not long withstand even the slight handling necessary for 
measuring them. In most of the plants the terminal portion began to die off 
in less than a week’s time. 
Ilea fulvescens is a second alga that is associated almost exclusively with 
fresh-water inlets of the Inner Harbor. This species forms smoky, olive 
green or brown flexuous threads, about 1 mm. in diameter and from 5d to 10 cm. 
long. It is found streaming from pebbles of the bottom, in the swiftest current, 
of these streams at levels between 1.5 and 7 feet above mean low water. It 
occurs most abundantly in the Creek, where in most years it covers many 
square meters of the bottom. In larger rivulets of the west shore Jlea has been 
found in one or two summers on constantly submerged pebbles between the 
6 and 7-foot levels. It has also been found at one or two points on the south 
shore of the Spit. But here, instead cf forming free streaming filaments, we 
find short threads of the I/ea, apparently in living condition, felted in with the 
other alge that coat the pebbles of the beach between the 6 and 7 foot levels. 
Why an alga so abundant each summer in the main stream should be rela- 
tively so scarce in the other streams about the harbor, it is difficult to under- 
stand. Apparently the conditions are closely similar in the two cases. On the 
other hand, it is not easy to see what common factors or conditions may 
determine the occurrence of this alga both in the fresh-water streams and on the 
beach of the Spit, since the latter is absolutely devoid of fresh water except such 
as falls in rain. Jlea is apparently an early summer form in this harbor; at 
least it was entirely wanting in the main stream, and absent from one or two 
of its other habitats on September 28, 1911. 
