Further Observations on the Phytoplankton 
of the River Thames. 
BY 
F. E. FRITSCH, B.Sc., Ph.D., F.L.S., 
Demonstrator in Botany , University College , London. 
T HE present year, with its unusually great rainfall and 
consequent heavy floods, has not been very favourable 
for comparative investigations of the river Plankton. The 
disturbing influence due to the height of the water and the 
strength of the current has been very noticeable in some of 
the samples collected, especially in those of May 2 . The 
speed of the current on that day was quite four times the 
usual one, and it is a well-known fact that the quality of 
the Plankton is considerably dependent on the rate of the 
stream (cf. Zacharias, ’98, p. 46 ; Zimmer, ’99, p. 7 ) ; a con- 
tinuation of such conditions for several days would probably 
have a very considerable effect on the composition of the 
Plankton, and this would most likely last for some time after 
the restoration of the normal state of affairs. It is therefore 
probable that, although the main features of the periodicity 
are sufficiently evident, observations under more normal 
conditions would have disclosed a number of minor points 
which have been obscured this year. The object of the 
present paper is primarily to touch upon the main points in 
the periodical development of the Plankton of the River 
Thames. 
Detailed investigations of the periodicity of river Plankton 
as yet scarcely exist, although Schroder has examined the 
[Annals of Botany, Vol. XVII. No. LXVIII, September, 1903.] 
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