Algal Vegetation of Ponds on Hampstead Heath. 7 1 
near Harpenden, are (1) a relatively low temperature of the water 
(2) absence of competition between it and two other filamentous 
algae, CEdogonium and Conferva. In the Hampstead ponds, however, 
a low temperature does not seem to be a determining factor, for 
the amount of Microspora present in ponds IV and VII increased 
during a steady rise of mean temperature throughout March and 
April, 1912, and in ponds I, III, IV and VII filaments were present 
in more or less abundance, in May and June of the same year at 
still higher temperatures. In July, 1912, there was an unusual 
abundance of Microspora in pond VII in spite of a very high mean 
temperature. On the other hand, in October and November, 1913, 
Microspora has been found in pond III during weeks when the 
temperature had been steadily falling. With regard to the competi¬ 
tion factor, however, my observations, in the main, bear out those 
of Fritsch. The period of greatest abundance of Microspora is 
before that of the dominance of the Conjugate ; as the Conjugate 
increase, Microspora decreases in amount; towards the end of July, 
1912, when there was a local abundance of Microspora in pond VII, 
the Conjugatae had already entirely disappeared. On the other 
hand, CEdogonium though present, never appears to compete 
successfully with other forms in these ponds, and Tribonema has 
maintained itself successfully during the whole of the periods during 
which Microspora has flourished, but neither appears to have 
impaired the other. 
Draparnaldia has been of frequent occurrence, but is most 
abundant in the cold weather. It has been found attached by a 
network of rhizoids, to sunken logs of wood, to the submerged roots 
of grasses and other aquatics, and once forming an extensive beard 
upon the back of a snail ( Limnea sp.). It appears and disappears 
abruptly as does Ulothrix, and on the logs of the cascades is often 
associated with Chcetophora, or with Vaucheria. In the former case, 
Draparnaldia appears to gain the ascendancy, and crowd out the 
Chcetophora ; in the latter case Vaucheria with its dense matted 
filaments often suppresses the Draparnaldia. 
The Stephanokont/e. 
This group is principally represented in the ponds by two 
species of CEdogonium , l one of which was observed to form oospores 
in June, 1912, but not in abundance. It has rarely been found to 
predominate in the vegetation of any pond, though it was dominant 
1 A third species, CEdogonium ciliatum, has been seen once only. 
