7 2 
E. Marion Delf. 
locally in VI1 (February, 1912), and in I (June, 1912). It has 
diminished markedly in amount during the whole of 1913, although 
it has often been found as part of the soft scummy matter which 
collects around the stems and leaves of submerged aquatic phanero¬ 
gams, and frequently as a number of sporelings attached to the 
surface of some submerged object. 
(Edogonium was most abundant in these ponds in 1912, during 
the dominant phase of the Protococcales, Flagellata and Ulothricales. 
According to Fritsch, 1 it tends to predominate during warm weather 
and bright sunshine in the Barton Pond, but in the Hampstead 
ponds it was most abundant in the colder months of the year 
(January to March), although the fruiting period (June, 1912) was a 
period of unusual warmth, and moderate rainfall and sunshine. 
In several cases, when samples of the algal flora of one of these 
ponds have been kept under observation for a number of weeks or 
months, Edogonium was ultimately found to dominate every other 
filamentous form, although scarcely to be found at first. On February 
26th, 1912, a sample of water from pond III was found to contain 
principally Spirogyra and Ulothrix , but also a very little (Edogonium , 
Mougeotia, and a few of the Protococcales. It was placed in a 
large glass jar with plenty of water, and examined some months 
later. In July the Protococcales had disappeared, as well as 
Ulothrix : the original species of Spirogyra (S. bellis ) had persisted, 
but two other much smaller species had also established themselves. 
In the following January, an examination of the same jar shewed 
that the Spirogyra had been entirely replaced by the (Edogonium 
which had been present in small amount from the first. Such 
observations suggest that Edogonium suffers from competition, 
especially with the Conjugate; but from some other observations 
on Edogonium during zoospore formation, it seems probable to me 
that the large zoospores, and even the young filaments, are often 
eaten by such aquatic insects as Asellus, which is an inhabitant of 
all the ponds. It is not possible to account for the entire lack of a 
fruiting period in 1913 as compared with 1912. 
The Heterokontve. 
Two species of Trihonema occur, of which T. bombycina is by 
far the commonest. The records apply mainly to this species, 
which is, however, sometimes accompanied by T. affinis in smaller 
amount. Vaucheria sessilis and V . geminata have both been observed, 
' Fritsch, F. E., and Rich, F. Loc, cit., pp. 26-30. 
