Algae. 17 



mids as a whole. The presence of numerous Desmids in the 

 plankton of the lakes follows as a matter of course. 



Neither plankton Desmids, nor those wnich occur in other situa- 

 tions, undergo any seasonal form-variation. 



Finally, the authors comment upon the cosmopolitanism of the 

 freshwater plankton-community, except as regards Desmids. For 

 that group they find that wherever there are lakes with a rieh 

 Desmid-Flora in the plankton, there one also gets a more or less 

 definitely localised plankton-community. They recognise at least 

 three distinet plankton-communities, which can be at once distin- 

 guished from one another, and which form a most interesting com- 

 parison. These are 1) the Desmids of the British (and to a certain 

 extent of the Scandinavian plankton, 2) the Desmids of the 

 plankton of Victoria Nyanza, and 3) the Desmids of the Victo- 

 rian plankton (as exemplified by the Yan Yean Reservoir). 



The paper contains three text-figures. E. S. Gepp. 



West, W. and G. S., The Phytoplankton of the English 

 Lake District. (Illustrated). (The Naturalist. April 1909. 627. 

 p. 134-141. 1 fig. May 1909. 628. p. 186-193. 1 fig. 1 chart. July 

 1909. 630. p. 260-267. 1 fig.) 



These three contributions continue the work begun in a pre- 

 vious number. In the first is continued the detailed description of 

 the individual lakes and tarns; and then follows a table of phyto- 

 plankton shewing the distribution of species in parallel columns. 



In the second paper the authors describe the periodicity of the 

 plankton of Lake Windermere month by month during an entire 

 year, and follow this by some general remarks upon Periodicity. In 

 Windermere the dominant constituents are Chlorophyceae and Dia- 

 toms, the Myxophyceae never at any time being conspieuous. In 

 all, 65 species have been observed, of which 30 are Chlorophyceae , 

 23 Bacillarieae , 7 Myxophyceae, 3 Flagellata, and 2 Peridineae. The 

 plankton of Windermere has three fairly distinet phases: I: Ja- 

 nuary to April (cold period). Melosira granulata phase. During 

 February and March the phytoplankton is at its maximum. II. May 

 to July (vernal rise of temperature). First maximum of Asterionella 

 gracillima in May and June. The Crustacea are dominant in July. 

 III. August to December (autumnal fall of temperature). The Desmid 

 phase extends from August to November, and is most noticeable in 

 September and October. In November is a second maximum of 

 Asterionella gracillima. The Crustacea are dominant in August. 



The Entomostraca reach a maximum towards the end of August, 

 thus following immediately after the enormous maximum of Asterio- 

 nella gracillima in May and June. This affords confirmatory evidence 

 of the conclusion arrived at by Kofoid that Asterionella is one of 

 the primary sources of food of the Entomostraca. 



The Chlorophyceae attain their maximum abundance in Septem- 

 ber and October, which fact is in close agreement with the greatest 

 abundance of Chlorophyceae in the Central European lakes. 



All the Desmids attained their greatest abundance during the 

 autumnal fall of temperature. The same was also true of the Proto- 

 coeeoideae, but no species of this order ever became really common. 

 The maximum abundance of plankton-Desmids oecurs in late Sep- 

 tember or early October in almost all the British lakes. 



The Diatoms do not attain a universal maximum at one definite 



Botan. Centralblatt. Band 113. 1910. 2 



