Wes^ : Phytoplanktoii of English Lake District. 191 



The Entomostraca reach a maximum towards the end of 

 August, about the period of highest water-temperature, in 

 consequence of which during this period, the greatest actual 

 bulk of plankton is collected in the nets. 



The plankton of Windermere has three fairly distinct 

 phases, which can be stated as follows : — 



L — January- April (cold period). Melosira graniilata 

 phase. During February and March the phyto- 

 plankton is at its minimum. 

 II. — May-July (vernal rise of temperature). First maxi- 

 mum of Asterionella gracillima in May and June. 

 The Crustacea are dominant in July. 

 III. — August- Dec ember (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. 



It will be noticed that the great increase of the Entomostraca 

 follows immediately after the enormous maximum of Asterion- 

 •ella gracillima in May and June. This affords confirmatory 

 evidence of the conclusion arrived at by Kofoid * that Asterion- 

 ella is one of the primary sources of food of the Entomostraca 

 Bosmina, Daphnia, Cyclops, and Diaptomus. 



Chlorophyce^. The Green Algae attain their maximum 

 abundance in September and October, i.e., at the end of the 

 summer period and the beginning of the autumnal decline in 

 temperature. This is in close agreement with the greatest 

 abundance (July to the middle of October) of Chlorophycese 

 in the Central European lakes, as recorded by Schroder, f 

 Lemmermann,! and many others. 



In the April plankton numerous filaments of Ulothrix 

 zonata occurred, doubtless carried into the lake by floeds 

 in the feeding streams and becks. 



All the Desmids attained their greatest abundance during 

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



* C. A. Kofoid, ' The Plankton of the IlUnois River— 1894- 1899,' Bull. 

 111. State Lab. of Nat. Hist., May 1908, vol. VIII., art. i, p. 



t B. Schroder, ' Das Pflanzenplankton preussischen Seen ' in Seligo's 

 TJntersuch. in dem Stuhmer Seen, Danzig, 1900. 



I Lemmermann in ' Forschungsb. Biol. Stat. Plon,' X., 1903 ; in ' Zeit- 

 schrift fiir Fischeri,' XL, 1903 ; etc. 



1909 May I. 



