328 JVesl : Phytoplankton of Eriglish Lake District. 



The British lakes are remarkable beyond all other European 

 lakes (with the possible exception of the Scandinavian) in the 

 richness of their Desmid-flora. We have elsewhere discussed 

 the possible connection between this abundance of Desmids 

 and the Older Palaeozoic and Precambrian strata which form 

 the great mass of the rocks constituting the drainage-basins 

 of so many of these lakes. It also seems highly probable that 

 the chief determining factor in this richness is a chemical one. 



Bachmann, in his remarks upon the Desmids of the Scottish 

 plankton, makes the mistake of generalising from a few samples. 

 He states that Desmids seldom form a dominant feature of the 

 plankton, and that a Desmid-plankton is only characteristic 

 of small lakes. Both these statements are quite erroneous con- 

 cerning the plankton of any of the British lake-areas 



The following table will give some idea of the abundance of 

 Desmids in the British lakes as compared with some of the lakes 

 of Continental Europe. The numbers are percentages of the 

 total species observed in the phytoplankton. The percentages 

 of Bacillariese and Myxophycete are also given for comparison. 



In the English lakes there are relatively few Protococcoideae, 

 and no species can be described as common. Glceocystis gigas 

 and Sphcerocystis Schroeieri are the most generally distributed 

 species, but even they are rarely abundant. There is an entire 

 absence of Pediastrum simplex and P. duplex, and also of the 

 genus Kirchneriella. f 



* The percentages given for the Swiss and Scandinavian lakes are only 

 approximate. The percentages of the three groups in the German lakes 

 have not been accurately ascertained, but the percentage of Desmidiaceae 

 is low (under 10%) whereas the percentages of Bacillariese and Myxophycese 

 are very high. 



t The absence of Kirchneriella from the plankton of the English lakes 

 is rather remarkable, as the commonest British species — K. obesa W. & 

 G. S. West (in ' Journ. Roy. Micr. Soc.', Feb. 1894, p. 16)— was first des- 

 cribed from small ponds near Bowness under the name of ' Selenastruni 

 obesnm ' [vide West, ibid., Feb. 1892, p. 22). 



Naturalist, 



