^Vesi : Phytoplankton of English Lake District. 117 



In all, eighteen lakes were examined for their phytoplankton, 

 the tow-netting being done by boats wherever they were avail- 

 able. Where boats could not be obtained, the plankton- 

 collections were made either by the tedious process of baling a 

 large volume of water through the nets, or by allowing the water 

 of the outlet to flow through the nets for some time. The nets 

 used were such as we have described before, and consisted of 

 the strongest silk bolting-cloth, with a very close and imiform 

 mesh (170 meshes in a linear inch). 



We have quite recently been receiving regular monthly 

 •collections from Windermere, Wastwater, and Ennerdale 

 Water, in order to obtain an adequate idea of the periodicity 

 •of the various constitutents of the phytoplankton of three 

 representative lakes. As yet, only the Windermere collections 

 are complete for twelve months, and a separate section of this 

 paper is devoted to their consideration. 



II.— DETAILED ACCOUNT OF THE LAKES EXAMINED. 



General Notice of the Lakes Investigated. The dates 

 are those on which the plankton-collections were made. 



1. Buttermere, Cumberland. May 1903. Altit. 331 feet. 

 About one and a quarter miles long, by three-eighths of a mile 

 broad. Average depth about 55 feet ; maximum depth, 94 

 feet. The lake is in the midst of mountains, and lies quite away 

 from any village. The plankton contained a few good Desmids 

 and a quantity of Peridiniiim Willei. Tabellaria fenestrata was 

 the most conspicuous of the Diatoms, and of the Rotifers, 

 Notholca longispina was abundant. 



2. Crummock Water, Cumberland, May 1903. Altit. 321 

 feet. About two and a half miles long, by five-eighths of a mile 

 broad. Average depth, 88 feet ; maximum depth, 144 feet. 

 The lake is in the vicinity of high mountains, one summit having 

 an altitude of 2791 feet, being distant less than one mile. There 

 are no villages in the vicinity, and therefore little contamination 

 of the water. The plankton collected could be described as a 

 DiNOBRYON-PLANKTON. The dominating species was Dino- 

 bryon cylindricum, and with it was a quantity of Coelosphcsrium 

 Kiitzingianum. Theoonly conspicuous Diatom was Melosira 

 granulata. Of the Chlorophyceae, Ankistrodesmns Pfitzeri was 

 quite common, a sterile species of Mougeotia with very long 

 cells was frequent, and a number of Desmids were of general 



1909 March i 



