259 



The Development of Vegetation in the English Lakes, considered 

 in relation to the General Evolution of Glacial Lakes and 

 Rock Basins * 



By W. H. Peaesall. 

 (Botany Department, University of Leeds.) 

 (Communicated by A. G. Tansley, F.E.S. Eeceived April 28, 1921.) 



Inti'oduction. 



During the past seven years, 1913-20, a large number of observations 

 have been made in the English Lakes in an attempt to obtain some 

 knowledge of the life conditions of aquatic plants. While the immediate 

 object was to obtain light on the factors governing the distribution of these 

 plants, it was also hoped that the results might bear upon more general 

 problems of aquatic biology. The considerable data thus obtained, though 

 far from complete, seem to be of interest from both these points of view. 

 They are also capable of a more general interpretation, which is here 

 attempted, and which, for the sake of clearness, may be indicated at this 

 stage. 



It is assumed that lakes and lake basins become modified as they increase 

 in age. Evidence is then presented for considering the English Lakes as a 

 series illustrating this process of lake development, and an attempt is made 

 to describe the phases in this process, and to relate the marked differences in 

 lake vegetation and fauna to the stages in the topographical evolution of 

 a lake. 



The data given below refer to the normal summer conditions of these lakes, 

 and the methods employed in obtaining them have been described in a 

 previous paper.f The ardiious work of surveying the lake shores has only 

 been possible through the unsparing assistance of my father, W. Harrison 

 Pearsall, to whom I am very greatly indebted. The water analyses given 

 were undertaken by Messrs. A. W. Eichardson and E. Jaffe, to whom my 

 thanks are due. 



General Features of the Lakes and Lake Area. 



The English Lakes lie among the high hUls of Cumberland, Westmoreland, 

 and North Lancashire. These hills consist essentially of a central uphft, 



* The cost of this investigation has been defrayed in part by grants from the Royal 

 Society. 



t Pearsall, " The Aquatic Vegetation of the English Lakes," ' Journ. Ecol.,' vol. 8, 

 1920. 



VOL. xcn. — B. X 



