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A STUDY OF SOME OF THE FACTORS 
CONTROLLING THE PERIODICITY OF 
FRESHWATER ALGiE IN NATURE 
By WILLIAM J. HODGETTS, M.Sc. 
(With ii figures in the text) 
I. INTRODUCTION 
T his paper deals with the periodical phenomena of the algal vege¬ 
tation of a small freshwater pond. The research was undertaken 
not only for the purpose of elucidating the periodicity of the chief 
algal species present, but also with the object of demonstrating what 
dependence, if any, exists between the development and reproduction 
of the various Algae, and the meteorological and other conditions, 
special attention being paid to the part played by the concentration 
of the water. Throughout the paper the principle of limiting factors 1 
has been employed in discussing the influence of these various 
external conditions upon the growth and reproduction of the Algae 
of the pond. The pond chosen is situated near Hawkesley Hall (and 
thus in the sequel is termed Hawkesley Hall Pond), i|- miles from 
King’s Norton, near Birmingham, and the observations extend over 
a period of 3J years, namely from January 1918 to June 1921, and 
are based upon numerous samples collected at monthly (at times 
fortnightly) intervals. 
The pioneer work on algal periodicity, as observed in small ponds, 
was commenced in this country by F. E. Fritsch ( 13 , 14 ), and later 
Fritsch and Rich published a series of “Studies on the Occurrence 
and Reproduction of British Freshwater Algae in Nature” ( 16 , 
17 , 18 ). Many of the conclusions arrived at by these workers have 
been confirmed by the present writer in the observations recorded 
below. Other contributors to the study of algal ecology in this 
country are G. S. West ( 31 ), and also W. and G. S. West ( 32 , 33 , 34 ), 
although the papers quoted of the latter authors deal mainly with 
the periodicity of the phytoplankton of British lakes. The compara¬ 
tively recent account of the occurrence of freshwater Algae in nature 
by the late Prof. G. S. West ( 31 , pp. 418 - 451 ) is a useful though neces¬ 
sarily short resume of our knowledge of the subject up to 1916. 
B. M. Griffiths ( 19 ) has studied the algal conditions of a pool near 
1 A principle first utilized in algal ecology by Fritsch and Rich (16, 17, 18). 
