Algal Vegetation of Ponds on Hampstead Heath. 65 
were usually examined at once and recorded in a suitable register. 
When floating masses of algae could be seen these were sampled in 
different parts of the same pond, and the local variations of the 
same piece of water were sometimes very surprising. Shoots of 
submerged plants and decaying leaves or stalks were very often 
examined for epiphytic forms, or fortangled filaments. Frequently 
the filamentous algae seem to appear in this manner for a time, and 
then to gradually increase in amount until at last they float upwards 
as detached masses often of considerable size. Occurrences of 
animal and insect life have been noted, but the data are not yet 
sufficiently comprehensive to be included in the present account. 
Fig. 2. Photograph of Cascade II, taken July 8th, 1913, 
There is, on the whole, a distinct periodicity in the algal 
vegetation, the two principal periods being the early winter months 
(October to December) and the early spring months (February to 
March or April). The latter phase is the more important, and 
usually exhibits a predominance of the genera Spirogyrn, Mougeotin , 
Tribonema and Microspora, under the shelter of which a great 
variety of unicellular and colonial forms occur. The early winter 
phase is much less distinctive both in variety and amount, but there 
is no very sharp line between the early winter and the vernal 
vegetation. 
In addition to those algae which reappear periodically; there 
are some, such as Scenedesmus, which have only been found 
