164 William J. Hodgetts 
during July and August. In the autumn (Edogonium gradually 
decreases in amount, and by November has generally become rather 
scarce; but the Zygnema again develops during September and 
October, and in general shows a steady increase up to the following 
spring maximum. 
In the Shallow-water Province, however, rather more species are 
concerned in the annual cycle. Roughly three phases can be dis¬ 
tinguished each year, and of these the spring-phase coincides (as 
regards the season) with the spring-phase observed in the Central 
Province. The three phases are: 
(< a ) a vSpring-phase (February to May) with Sfiirogyra spp. pre¬ 
dominating, and Tribonema bombycinum gradually decreasing, while 
Mougeotia scalaris may be locally common during May; 
(b) a Summer-phase (June to September) with Anabcena 1 
dominant, and Cylindrospermum locally common; and 
(c) a late Autumn and Winter-phase (October to January) with 
Tribonema bombycinum the chief species, while Spirogyra spp. may 
be locally common, and Microspora more or less developed during 
the winter. 
There is much more variation in the annual cycle shown by the 
Algae of the shallow marginal region than in that observed in the 
Central Province of the pond, and this variation can in many cases 
be explained by a consideration of the various factors (temperature, 
concentration of the water, bright sunshine, etc.) which control to a 
large extent the growth of freshwater Algae in nature. This matter 
will be discussed in the following sections. 
Perhaps the most obvious point of distinction between the general 
annual cycle of the algal vegetation of Hawkesley Hall Pond and 
that described by Fritsch and Rich, both in the case of Abbot’s 
Pool ( 17 ) and also Barton’s Pond(i8), is the absence of any distinct 
Diatom-phase during the colder months in the pond now under 
consideration. Diatoms never played more than a mere subsidiary 
part in Hawkesley Hall Pond, although a fair number of species were 
observed in it. 
The more detailed discussion of the periodicity of the chief algal 
forms represented in the pond now comes under consideration. 
1 Anabcena also extends into the deeper water during the summer 
months. 
(To be continued .) 
