84 МК. G. S. WEST ON THE FRESHWATER ALG 
June 1904, and is chiefly interesting in comparison with material collected 
by Dr. Fülleborn (1898-1900) and reported upon by Schmidle*. In 
Victoria Nyanza the material was collected in April 1905, and again the 
chief interest lies in a comparison with Schmidle's report f upon material 
collected by Dr. Stuhlmann in Oct. 1892. From Tanganyika, however, the 
collections were much more extensive, ranging from July 1904 to Feb. 1905, 
and this is the more gratifying as there are no previous records of phyto- 
plankton from this lake. 
The phytoplankton of these large African lakes is at once peculiar in the 
absence of many genera which are a dominant feature of the European lake- 
plankton. Most noticeable in this respect are the genera Dinobryon, Asterio- 
nella, Tabellaria, Rhizosolenia, and Colospherium. Schmidle has already 
commented f upon the absence of Dinobryon from Lake Nyasa, and it is 
similarly absent from both Victoria Nyanza and Tanganyika. In temperate 
Europe and N. America this genus is one of the most conspicuous of plankton- 
organisms, having a well-marked maximum period, and it also occurs in 
abundance in the lakes of more northern latitudes. Its absence from the 
plankton of the tropics is perhaps due to unsuitable conditions of temperature, 
as this genus appears to attain its maximum in the European plankton at a 
temperature below 15° C., whereas the mean temperature of Tanganyika is 
about 24:7? С. The absence of Asterionella and Jhizosolenia may be due to 
the same cause, viz., too high a temperature, the latter genus attaining its 
maximum in certain European lakes at a temperature below 10? C. The 
genus Tabellaria is absent from the plankton, but Tabellaria floceulosa has 
been observed from other situations in Angola, W. Africa. 
Spherocystis Schroeteri is also absent from the collections of phytoplankton 
which have so far been made in these great African lakes, and as Schmidle 
has also commented upon its absence from the plankton of Lake Nyasa $, 
even from collections extending over a period of ten or eleven months, it 
would appear that the Alga in question is entirely absent from this lake. It 
is likewise absent from the Tanganyika collections, which are fairly repre- 
sentative of eight months of the year; but, strange to say, it occurred in great 
abundance in two samples of plankton from the Lofu River which runs into 
Tanganyika. 
The Desmidiace: are poorly represented in the plankton of Tanganyika 
and Lake Nyasa, but in the plankton of Victoria Nyanza Desmids play a 
conspicuous part. This was not only the case in Dr. Cunnington's material 
collected in April 1905, but also in Dr. Stuhlmann's material collected in 
October, 1902 ||. The plankton of Victoria Nyanza thus compares favourably 
* W. Schmidle, in Engler, Bot. Jahrb. xxxii. (1903). 
t W. Sehmidle, 7. c. xxvi. (1898). t W. Schmidle, 7. с. xxxii. (1903) р. 8. 
$ W. Schmidle, 7. c. xxxii. (1903) p. 8. | W. Sehmidle, 7. c. xxvi. (1896) p. 6 
