Periodicity of Freshwater Algce in Nature 151 
Kidderminster, and E. M. Delf (12) has given an account of the algal 
periodic^ observed in ponds on Hampstead Heath; while conti¬ 
nental workers on the periodicity of freshwater Algae are Comere 
(6, 7 , 8), Rabanus ( 26 ), and also Pevalek ( 24 ). Reference will not be 
made to all the workers who have investigated experimentally the 
relation between the growth of Algae and various cultural conditions, 
as many of these artificial conditions are never realised in nature— 
although, as pointed out by Fritsch ( 14 ), they may be paralleled. 
The chief American worker on the subject is E. N. Transeau 
( 27 , 28 ), who has published results based on 7J years continuous 
records of the algal conditions in Central Illinois; while other 
American contributors are H. B. Brown ( 4 ), Copeland ( 9 ), Platt ( 25 ), 
and more recently Andersen and Walker(l). Various workers in 
America have investigated the relation between algal growth and 
the dissolved gases of the water, and in this connection reference 
may be made to the interesting papers of Birge and Juday ( 3 ), and 
Chambers( 5 ), further literature being cited by these authors. 
It has not been thought necessary in a paper of this sort to refer 
to all the numerous workers who have contributed to our knowledge 
of the freshwater phytoplankton, since this constitutes rather a 
special branch of algal biology, requiring methods of attack some¬ 
what different from those adopted in the present line of research; 
but papers on the freshwater plankton, are occasionally referred to 
in what follows. As pointed out by Fritsch and Rich ( 18 ), and 
West ( 30 ), the smaller pieces of water are alone suitable for demon¬ 
strating the relations between external conditions and algal growth, 
since larger bodies of water react much more slowly to variations 
in the meteorological and other conditions than do ponds and small 
bodies of water generally. 
II. GENERAL ACCOUNT OF HAWKESLEY HALL POND 
AND ITS PHANEROGAMIC FLORA 
Hawkesley Hall Pond is situated in a meadow about J mile N.W. 
of Hawkesley Hall, and is not at all large, its area, when the height 
of the water is at a maximum, being roughly 300 sq. metres, while 
the greatest depth, although not known exactly, is probably between 
i-J and 2 metres. It is an irregular triangle in shape (cf. Fig. 1), 
with the marginal banks for the most part rather low, and almost 
all round the pond bearing a thick growth of rushes, together with 
other Phanerogams (see below). There are no trees at the margin of 
the pond, the nearest being a few oaks by the fence (shown in Fig. 1) 
