The Development of Vegetation in the English Lakes. 275 



emergent species, P. natans, with the Uquisetum-Carex type of reedswamp, 

 predominate, though Scirpus and Phragmites are also abundant. The same 

 plants are characteristic of Hawes Water and Bassenthwaite, though much 

 less abundant. In Coniston and Windermere, Scirpus and Phragmites are 

 more typical, along with some P. natans. In Esthwaite, water-lilies and 

 Phragmites fringe most of the western shore. On the whole, as silting 

 conditions improve, water-lilies and Phragmites tend to become more 

 abundant in the lake series, a fact in agreement with their distribution on 

 relatively inorganic soils, which are relatively richer in K2O.* P. natans, 

 Equisetum and Carex inflata, on the other hand, are found on highly organic 

 soils, relatively poor in K2O. Obviously, the increased development of 

 finer and richer silts in evolved lakes tends to prevent the formation of 

 these highly organic soils, except in land-locked and stagnant bays — which 

 are uncommon in this lake area. It is therefore primarily to the silting 

 factor that the development of both deep and shallow water vegetation is due. 



General Conclusion. — This detailed discussion shows clearly that the 

 fundamental factor in the development of the attached vegetation is the 

 increase in abundance and richness of the sediments. Not only does this 

 control the types of plant communities found, but it also limits the quantity 

 of vegetation produced. Vegetation is sparse in the primitive lakes ; it 

 becomes increasingly abundant in the evolved lakes. As was suggested at 

 the conclusion of the last section (p. 267), the lake series viewed in this way 

 enables us to reconstruct the stages in the post-glacial development of these 

 lakes. If this be done for the vegetation, we obtain the following means for 

 the four main types of lake, and these represent four stages in the develop- 

 ment of a post-glacial flora : — 



Vegetation Types. 





Type of lake. 





I. 



II. 



III. 



IV. 





Primitive (4) . 



Intermediate (3). 



Evolved (3). 



Esthwaite. 



Primitive plants — 













80 -5 



65 



47-6 



30 



Juncus and CallUriche 



9-4 



11 -9 



3-1 





(requiring coarse silts) 











Potamogeton spp. (re- 



1-0 



4-6 



31 -3 



25-5 



quiring finer silts) 











Naias, Sydrilla and 







3-0 



21 -0 



JSlodea 











VOL. XCII. — B. 



* Pearsall, loc. cit. 



Y 



