342 FRESH-WATER ECOLOGY 



(c) Zone 0-3-5 ^^- No definite community is formed in this 

 belt. 



(d) Zone 2-3-5 "^- ^ distinct community dominated by 

 Cyanophyceae. 



(2) Epiphytic communities growing on aquatic macrophytes : 



(a) On submerged plants between o and 0-5 m. This possesses 

 a conspicuous Chlorophycean element, e.g. Conjugales, 

 Chaetophorales and Ulothricales. 



(b) On submerged plants between i and 3 m. dominated by 

 Oedogonium^ Coleochaete and diatoms. 



{c) A community on submerged plants between 3 and 6 m. 

 which is comprised of Coleochaete^ a few diatoms and some 

 Cyanophyceae. 



(3) Communities on dead leaves and organic debris: 



{a) Between o and 12 m.: wholly Diatomaceae. 

 {h) Between 2 and 16 m.: four diatom species and Microcoleus 

 delicatulus. 



The depth range of the diatoms was found to be greatest at the 

 time of their maximum in spring and smallest in mid-winter. It 

 was also discovered that the diatom frequency and light intensity 

 often show an opposite trend in the upper layers and a similar 

 trend in the lower layers of the lake. The nature of the habitat, 

 whether organic or inorganic, makes a considerable difference to 

 the behaviour of the different species, and each individual species 

 responds to the differences of these two environments in its own 

 way. In spite of these differences, however, they all exhibit an 

 April maximum and depth has the same influence on them all 

 (cf. fig. 200). A study of the plankton of Lake Windermere gave 

 results that were in accordance with the view that the constituents 

 of the floating community originate from the algae of the littoral 

 region. 



The periodical development of the littoral algal flora can be 

 summarized as in Table XVII. 



A study of the chemistry of the waters in the different algal 

 habitats around the lake is summarized in Table XVIII. 



An investigation of the distribution of the algae in relation to the 



