?6 
E. Marion Delf. 
for food, although they speedily demolish all signs of CEdogonium, 
Ulothrix and various other green algae: this may perhaps account 
for the ease with which this genus persists through the months of 
April, May and even June, when these ponds are teeming with the 
most diverse animal life. 
A peculiar species of Spirogyra has been observed attached to 
the logs of one of the cascades. In spite of many observations in 
the field and numerous culture experiments, it has never been found 
in conjugation, but the sterile filaments closely resemble those or 
S. adnata. 1 This is distinctly a summer form and has only been 
found from July to November, 1912, and very scantily in June and 
July, 1913. It was most abundant in July and August, 1912, and 
disappeared entirely in December of that year, being apparently 
suppressed by a luxuriant growth of Draparnaldia. The filaments 
are curious in being attached to the substratum by much branched 
rhizoids, which become very stout and thick. In one case a filament 
was found the rhizoids of which had clasped a neighbouring filament 
of Vaucheria with many delicate finger-like processes (Fig. 3); in 
other cases the central cells of a filament were fastened down by 
rhizoids, the two ends trailing freely in the running water. 
The seasonal activity of Spirogyra has been fully discussed by 
Fritsch. 2 According to this author, there is usually a well-marked 
vernal phase in the later spring months, a more or less complete 
disappearance of the filaments in the summer months and a secondary 
autumnal activity in some cases ( e.g ., in Abbot’s Pool), probably 
whenever the summer conditions allow a few vegetative filaments 
to persist unharmed. In the Hampstead ponds most of my obser¬ 
vations are in accord with these views. There has been a late 
autumn or early winter period both in 1912 and 1913, but never as 
well-marked as the spring maximum. In 1912 there was a long 
and striking vernal phase, but the autumn phase was insignificant; 
in 1913 the vernal phase was much less striking than in the preceding 
year and no conjugation was observed in the ponds, although zygo¬ 
spores were easily produced in the laboratory from the same material 
in May and June. The following autumn the filaments reappeared 
in October (ponds II, III and IV), in November (V and VIII) also 
in December (I and VI), and conjugation was observed on a bright 
’ See Delf, E. M. “On an attached species of Spirogyra." Annals of 
Botany, 1913. 
1 Fritsch, F. E., and Rich, F. “ Preliminary observations on Spirogyra.' 
Annals of Botany, 1907; “ Five years’ Observation of Fish Pond, Abbot’s 
Leigh.” Bristol Nat. Soc., 4th ser., II, 1909. 
