Algal Vegetation of Ponds on Hampstead Heath. 75 
and slightly brown. About ten days later the green zygotes began 
to turn brown and to sink, so that it became possible to distinguish 
two strata,—an upper green one where conjugation was still at its 
earliest, and a lower brownish one where the zygotes were nearly 
ripe. Later on the zygotes could be detected in the mud at the 
bottom of the pond (July, 1912, pond II). 
The different species of Spirogyra seemed to wholly disappear 
from the ponds during the months of July, August and September, 
both in 1912 and 1913. In each case they reappeared towards the 
end of October, at first as a few scattered filaments clinging around 
Fio. 3. Spirogyra (? adnata ), showing haptophores clasping a filament of 
Vaucheria. Drawn with Zeiss | lens. 
submerged vegetation, although not actually attached to it. Later 
in the winter the filaments increase in length and in numbers, and 
cell-division becomes active, especially after a hard frost; but the 
filaments never become as numerous as in the spring months when 
they dominate the whole of the algal vegetation, I have repeatedly 
observed that young tadpoles, snails, aquatic insects such as Asellzts, 
and various aquatic larvae, will not touch any species of Spirogyra 
