154 
William J. Hodgetts 
The second zone of Scirpus palustris and Glyceria fluitans is 
rather a mixed one, but for the most part these two species are 
co-dominant, although in places Scirpus palustris alone is dominant. 
Alisma Plantago occurs sporadically. This zone is absent altogether 
in places, while it rarely extends into water deeper than 20 cm. 
The third zone (of Sparganium) is very well-marked and extends 
practically all round the pond (see Fig. 1), and varies in width from 
45 to 120 cm.—the latter where the slope of the bottom is very 
gradual, as on the east side of the pond. 
All the central region of the pond is occupied by the Potamogeton 
natans —a plant which has an important influence upon the algal 
vegetation of the pond, as will be seen later. During the winter and 
early spring (November to March) the Potamogeton is dormant, but 
development commences usually in early April, and by the end of 
June, or in early July, a great part of the water-surface of the pond 
is covered by the floating leaves of this plant, the spaces between 
the leaves being generally occupied by floating masses of filamentous 
Algae. It flowers in June and July. In September its leaves gradually 
decay, while by the end of October all the leaves are dead, many 
being free and decaying in the water. 
The pond is very similar in its phanerogamic vegetation to those 
described by Walker ( 29 ), at Bramhope, near Leeds, all the zones of 
vegetation (except the second) occurring in Hawkesley Hall Pond 
being represented in the Bramhope ponds. Doubtless ponds of this 
type, with similar or nearly similar phanerogamic plants, are frequent 
in many parts of the country; they are certainly not uncommon in 
the midland counties. 
III. METEOROLOGICAL DATA 
The more important meteorological data for the purpose of this 
study are those of temperature, rainfall, and bright sunshine. At 
the time of collecting the monthly samples of Algae the temperature 
of the water and of the air near the pond were recorded, but these 
are not given here, since they have been found to emphasise rather 
too much merely temporary and often very fleeting temperature- 
conditions which by chance obtained at the time the samples were 
being collected. Of the three temperature-curves given in the lower 
part of Fig. 2 the uppermost gives the average maximum temperature 
of the air, and the lowest the average minimum for each month, 
while the middle curve gives the mean of these two; the data being 
taken from the official Monthly Weather Reports (Birmingham 
