Wes^ : Phytoplankton of English Lake District. 331 



by Huitfeldt-Kaas* that small depth is favourable and great 

 depth unfavourable to the development of plankton. On the 

 contrary, there is a very considerable phytoplankton and 

 zooplankton in Loch Morar, Inverness, f which is not only the 

 deepest lake (1017 feet) in the British Islands, but the eighth 

 deepest lake in Europe. Likewise the great African lakes have 

 an enormous phytoplankton, J with a depth exceeding 1300 

 feet in Tanganyika, of 1200 feet in Lake Nyasa, and of 620 feet 

 in Victoria Nyanza. Many facts tend to prove that the presence 

 of available food-constituents in the form of dissolved salts is 

 the principal determining factor in the quantitative develop- 

 ment of plankton, and that this may result from several causes, 

 not the least of which is the slight sewage contamination in 

 so many of the European lakes. 



DESCRIPTION OF PLATE V. 



Photomicrographs of Plankton from Ennerdale Water (x 100). 



I and 2, Peridinium Willei ; 3 and 4, Ceratium hirundinella ; 5, Xan- 

 thidium antilopeeum var. depanpevatum ; 6 and 7, Stanrastritm defectum ; 

 8, St. jaculiferum (biradiate form undergoing division). 



9-11, Peridinium Willei; 12, Ceratium hirundiyiella ; 13 and 14* 

 Staurastrum curvatum, (or St. dejectimi ? ) ; 15, St. loiisispiuum ; 16, 

 St. jaculiferum. (biradiate form) ; 17, St. furcigerum. 



DESCRIPTION OF PLATE VJ 



Photomicrographs of Plankton from Crummock Water (xioo)- 

 and from Derwent Water ( x 200) . 



I and 2, Dinobryon cylindricum (with immature resting spores) ; 3, 

 Melosira granulata ; 3, Stout form of Staurastrum anatinum. 



5 and 6, Dinobryon cylindricum, var. divergens ; 7, Cyclotella compta. 



DESCRIPTION OF PLATE VII. 



Photomicrographs of Plankton from Windermere (xioo), 

 Upper Photograph of June Plankton, and Lower one of September 

 Plankton. 



I and 2, Asterionella gracillima ; 3, Tabellaria fenestrata var. Asterionel- 

 loides. 



4, Asterionella gracillima ; 5, Tabellaria fenestrata var. asterionelloides ; 

 6 and 7, Xanthidium subhastiferum var. Murrayi ; 8, Spondylosium 

 pulchrimt var. planum ; 9 and 10, Staurastrum paradoxum var. longipes ; 

 II, St. ■jaculiferum. 



* Huitfeldt-Kaas, I.e., 1906, p. 185. 



t W. & G. S. West in ' Trans. Roy. Soc. Edin.', Vol. XLL, part III., 

 1905, p. 481 et seq. 



I G. S. West in ' Journ. Linn. Soc. Bot.', XXXVIII. , 1907, pp. 81-192^ 

 1909 Sep. 1. 



