Algal Vegetation of Ponds on Hampstead Heath. 73 
but the former is the commoner. Michococcus is a small epiphytic 
species which has only been seen in February, 1914. 
On the whole the Heterokontae show the same well-marked 
dominance in the vernal phase (February to May), but Tribonema 
persists in small amount almost throughout the year as a slight 
tangle of filaments around submerged plants in a way which suggests 
that it is probably perennial. When on the increase, the filaments 
appear to multiply freely, appearing at first as little flocculent masses 
around various submerged shoots—especially around Elodea. A 
little later soft pale green masses are found freely floating in the 
water, as has been seen in ponds I and IV, February and March, 
1912, and in V locally, in October to December, 1913. 
According to Fritsch, Tribonema flourishes best in the absence of 
sunlight, but is sensitive to competition, especially with Microspora. 
My observations bear out the shade-loving habits of the plant, for 
it is always most abundant in those regions in which it is sheltered 
by submerged vegetation. Although most abundant in the com¬ 
paratively dull months of February and March, it was yet common 
in ponds V and VII in June, 1912 and in May, 1913, these two 
ponds being deep in parts, and having many aquatic phanerogams, 
both marginal and submerged. In my experience there is no 
evidence that Tribonema suffers at all seriously from competition 
with either Microspora or any of the early spring filamentous algae. 
In the Hampstead ponds, however, it is apt to suffer from attacks 
of epiphytes, especially from Ascoglena and from species of Synedra 
and Gomplionema ; these epiphytes become especially numerous 
towards the end of a period of vegetative activity of Tribonema , 
the Ascoglena in the colder, and the Synedra in warmer weather. 
On the whole, in these ponds, Tribonema may be described as a 
probably perennial form with a well-marked maximum in February 
and March, and with a less distinctive secondary maximum in 
October and November. 
Vaucheria has been observed mostly on the logs which form 
the small cascades from one pond to another, attached firmly by 
numerous rhizoids to the somewhat sandy crevices of the wood. 
In April, 1912, V. geminata was found fruiting amongst matted 
filaments of V. sessilis. In February and March, 1913, V. sessilis 
was again found fruiting freely, but V. geminata was not seen. 
When the cascades dry up for a few days or weeks, the Vaucheria 
seems to disappear. Three or four days after the flow of water is 
resumed, Draparnaldia is commonly found, which is quickly followed, 
