U\'si : Phytoplankton of English Lake District. 329 



The Diatoms are very conspicuous in the plankton of some 

 of the EngHsh lakes, and although they are represented by only 

 one third as many species as the Chlorophyceae, they are often 

 the dominating constituents. Especially noticeable are As- 

 terionella gracillima, the two species of Tabellaria, and Melosira 

 graindata. 



Gomphonema geminatum occurred in fair quantity in the 

 plankton of Wastwater and of Hawes Water. We have also 

 recorded it quite common freely floating in Loch Tay.* This 

 species is normally attached and can be obtained in pure masses 

 in many of the mountain cataracts. Numerous individuals 

 evidently get washed down by heavy rains into the limnetic 

 region of the lakes, where they live for some time before perish- 

 ing. 



The Myxophyceae are almost as poorly represented as in 

 the Scottish lakes, the number of species being relatively few. 

 Coelosphcenum Kiitzingianum attained considerable abundance 

 in both Crummock Water and Hawes Water, but the genera 

 Lynghya and Anahcsna were barely represented, and species 

 of Oscillatoria were not frequent. 



Among the Flagellates the genus Dinobryon is conspicuous, 

 and so far as the English lakes are concerned, D. cylindricum 

 and its \'ar. divergens, are much the most abundant forms. 

 At the end of May and beginning of June, the three lakes, 

 Derwent Water, Crummock Water and Grasmere, possessed a 

 Z)mo&rvo n-plankton [vide plate VL). In Windermere the 

 maximum of Dinobryon cylindricum was in September 



Mallouionas longiseta occurred in great abundance in Sep- 

 tember in Brothers' Water, whereas the same organism attained 

 a decided maximum in December in Windermere. 



The most conspicuous member of the Peridiniese is Peri- 

 diniiim Willei. This organism is abundant in nearly all the 

 lakes, and occurs in much greater quantity than in either the 

 Scottish or Irish lakes. It is one of the leading features of the 

 plankton of the English Lake District. 



Among the numerous species recorded as constituents of 

 the phytoplankton of the English lakes, some are true con- 

 stituents, either not occurring elsewhere in the drainage-areas 

 of the lakes, or occurring much more abimdantly in the plank- 

 ton than in any other situations. The remainder are only 



* Vide ' Trans. Roy. Soc. Edin.', Vol. XLI., part III., 1905, p. 491. 

 1909 Sep. I. 



