165 



The British Freshwater Phytoplankton, with Special Reference to 

 the Desmid-plankton and the Distribution of British Desmids. 

 By W. West, F.L.S., and G. S. West, M.A., D.Sc, F.L.S. 



(Communicated by D. H. Scott, F.R.S. Received October 30, 1908,— Read 



January 28, 1909.) 



PAGE 



I. Introduction 165 



II. The Scottish Lakes 168 



III. Lakes of the Orkneys and Shetlands 170 



IV. The Irish Lakes (West and South-west) 171 



V. Lough Neagh 172 



VI. The Welsh Lake-area 173 



VII. The English Lake-area 174 



VIII. Malham Tarn, West Yorkshire 175 



IX. The British Eiver-plankton 175 



X. General Comparison of British Lake-areas 176 



XI. General Summary, and Discussion on the Dominance of Desmids ... 190 



I. Introduction. 



Not until much work had been done at the phytoplankton of the fresh- 

 waters of Western Europe were investigations of a similar nature begun in 

 the British lakes and rivers, and it is during the last ten years that almost 

 all our knowledge of this branch of freshwater biology has been acquired. 



We have ourselves conducted nearly all the British investigations, and 

 we now think the work has progressed sufficiently to enable us to 

 summarise the results, and to institute comparisons between the British 

 phytoplankton and that of continental Europe and other regions. 



Since 1900 we have collected plankton from a large -number of lakes in 

 the west of Scotland, from some of the lowland Scottish lochs, from 

 practically all the lakes of the English Lake District and most of those in 

 North Wales, from nearly all the lakes of the west and south-west of 

 Ireland, from Lough Neagh and Lough Beg, from Malham Tarn in West 

 Yorkshire, and from the Rivers Ouse, Lochay, and Bann. In the collection 

 of material for these investigations we have been greatly assisted by four 

 grants from the Government Grant Committee of the Royal Society and two 

 from the Fauna and Flora Committee of the Royal Irish Academy. 



From a biological standpoint the British lakes are of great interest, and 

 since the publication of the first reports on their plankton, the diversity of 

 the Algal constituents has been a revelation to the freshwater biologist. 

 In the number and diversity of the species constituting this phytoplankton 



VOL. LXXXI. — B. N 



