1 88 Wes^ : Phyioplankton of English Lake DistricL 



III.— THE PERIODICITY OF THE PLANKTON 

 OF WINDERMERE. 



01 the periodical collections of plankton we have been 

 receiving from three lakes of the English Lake District, only 

 those from Windermere have hitherto extended over a suffi- 

 cient length of time to enable us to draw up a report on the 

 periodicity of the plankton-constituents. These collections 

 commenced in September 1907, and were made at fairly regular 

 monthly intervals until August 1908. We are indebted to Mr. 

 Frank Holmes, of Bowness, for continuing to make the collec- 

 tions according to instructions, and also for recording the water- 

 temperatures at the time of collection. 



Monthly Statement of Plankton from 

 Sept. 1907 to Aug. 1908. 



September 1907. — Water-temperature I4.4°C. (=58° F.). 

 Mixed Crustacea and Desmid plankton. The Crustacea con- 

 sisted of Bosmina longirostris, Daphnia longispina, and others. 

 The Desmids were very conspicuous, more particularly the 

 following six species — Cosmarium subtumidum var. Klebsii, 

 Xanthidium subhastiferum var. Murrayi, Staurastrum curva- 

 tum, St. jaculiferum, and St. pavadoxum. The Diatoms were 

 mostly Tabellaria fenestrata var. asterionelloides , which was 

 present in quantity, and Asterionella gracillima. Dinobryon 

 cylindricum var. divergens was in moderate quantity, and 

 certainly more abundant than in any other month of the twelve 

 during which' collections were made. Ceratium hirundinella 

 and Peridinium Willei are both general. Rotifers numerous. 

 Ccelosphcerium Kiitzingiamim rather common. 



October 1907. — Water-temperature 9°C. (=48°F.). Largely 

 a Desmid plankton, the four most conspicuous species being 

 Xanthidium subhastiferum var. Murrayi, Staurastrum curvatum, 

 St. cuspidatum var. maximum, and St. paradoxum. Cosmarium 

 subtumidum var. Klebsii has practically disappeared. Small 

 colonies of Sphcerocystis Schroeteri are frequent. Ceratium 

 hirundinella is fairly general, but there is less Coelosphceium 

 Kiitzingianum. Rotifers numerous. Increase in quantity of 

 Asterionella gracillima. 



November 1907. — Water-temperature 7.2°C. (=45°F.). 

 Gradually becoming a Diatom plankton. Great increase in 

 the quantity of Asterionella gracillima. A number of littoral 

 Diatoms washed into the plankton, mostly belonging to the 

 NaviculacecB. The three following Desmids were still con- 



Naturalist, 



