NOTES. 
ALGOLOGICAL NOTES. VI. THE PLANKTON OF SOME ENGLISH 
RIVERS.— Unfortunately I have been unable to continue my investigations of 
Thames Plankton this year, although a few remarks on one or two samples which 
were taken in April and May will be found at the end of this note. The year has 
been a particularly favourable one for such work, as I imagine that the season has 
been almost absolutely normal. The object of this note is to describe some samples 
of Plankton taken from the Cam at Cambridge and the Trent at Nottingham during 
the month of August; as both were collected in the same week, they may be regarded 
as representing corresponding periodical phases in the Plankton of the two rivers. 
I was, however, unable to gather material in the Thames at the same time of the 
year, and consequently have had to fall back on samples collected in August, 1902, 
for purposes of comparison \ In respect of the strength of the current the Thames 
occupies a position almost midway between that of the other two rivers concerned, 
the rate of flow being markedly less than that of the Trent. The comparison of the 
Plankton of the three rivers is therefore an interesting one from this point of view 
alone. Zacharias 2 and Zimmer 3 have both shown that the rate of flow of a stream 
has a considerable influence on the quality of the Plankton. The latter finds that 
f das Potamoplankton sich dem Plankton eines Teiches seiner Zusammensetzung 
nach um so mehr nahert, je langsamer der Fluss fliesst.’ The slow-flowing Cam 
therefore should possess a Plankton approximately like that of a pond. Before 
proceeding to discuss this point in detail, reference must be made to the table, which 
shows the comparative composition of the Plankton of the Trent, Thames and Cam. 
The samples of Plankton were collected from an ordinary rowing-boat. The 
Trent material was collected on the stretch of river between Trent Bridge and the 
Great Central Railway’s bridge over the river at Nottingham; the current was a 
strong one, and it was no easy matter to row against it with the net out, and 
consequently part of the material was collected from a stationary boat with the tow- 
net playing out into the current 4 . The samples contained a very considerable per- 
centage of mud, and a certain number of the Diatoms were dead and represented 
only by the empty frustules, although living specimens of all the species mentioned 
in the table were to be found ; in these respects the Plankton recalled that of the 
1 Cf. Fritsch, Algol. Notes, No. III. Preliminary report on the Phytoplankton of the Thames ; 
Annals of Botany, vol. xvi, 1902, table. 
2 Das Potamoplankton ; Zoolog. Anzeiger, No. 550, 1898, p. 46. 
8 Das Plankton des Oderstromes; Ploner Forschungsber., Teil 7, 1899, PP* 4 > 7 * 
4 The samples obtained in this latter manner were, however, not nearly so satisfactory as those 
collected from the moving boat. 
