Phytoplankton of the River Thames. 639 
not reveal them in the main river itself, although Bacillaria 
was found in samples taken from below the lock at Tedding- 
ton. Possibly the salinity of the water in the shallow arm is 
greater than in the main river, although Pleurosigma Fasciola 
was observed in a sample taken from the latter at a later date. 
The first two of the above-named Diatoms have also been 
observed by Zacharias (’98, p. 44) in the Unter-Eider (near 
Rendsburg), the waters of which at this point are of a brackish 
nature. I have never met with Bacillaria before or after in 
the river. Stephanodiscus Hantzschianus , a common con- 
stituent of the Plankton in the warmer months and in the 
autumn, was frequently observed to be provided with numer- 
ous elongated needle-like processes at its margin ; such have 
been already described and figured by Schroder (’97, p. 488 
and PI. XXV, Fig. 1), although in the cases observed by me 
they were relatively far more numerous than Schroder’s 
figures indicate. They undoubtedly serve to heighten the 
floating capacity of the individual. The individuals of Nitz- 
schia sigmoidea , which were very common in some samples, 
were frequently covered by large numbers of epiphytic speci- 
mens of Amphora minutissima, whose occurrence in the 
Plankton is thus due to its attachment to a larger form. 
Finally the occurrence of Goniuni pectorale in the samples 
of June 30 is noticeable, it not having been observed in the 
river before this. 
In the following portion of this paper I propose to give 
an account of the flora of some of the backwaters of the 
Thames between Chertsey and Teddington, of which on 
the whole there is a remarkably small number. I have 
already previously pointed out (Fritsch, ’02, p. 578), that 
the Plankton such as we find it in the main stream, although 
capable of a certain amount of multiplication, must to a great 
extent be stocked from other places, namely from the back- 
waters and slow-flowing tributaries of the river’s course. The 
presence of these backwaters is of immense importance from 
the point of view of the fisheries, for it is on the Plankton 
that the smaller fish, which furnish the food for the larger 
