368 THE ALGAE 



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

 belt. 



(d) Zone 2-3-5 m. A distinct community dominated by 

 Myxophyceae. 



(2) Epiphytic communities growing on aquatic macrophy tes : 



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

 sesses a conspicuous Chlorophycean element, e.g. Con- 

 jugales, 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, b. few diatoms and 

 some Myxophyceae. 



(3) Communities on dead leaves and organic debris : 



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



(b) Between 2 and 16 m.: four diatom species and Micro- 

 coleus 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 Hght 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 be- 

 haviour of the different species, and each individual species re- 

 sponds variously to the differences of these environments (Round, 

 1957). In spite of these differences, however, they all exhibit an 

 April maximum and depth has the same influence on them all (cf. 

 Fig. 201). 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 Tables 1 1 and 1 1 A. 



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

 habitats around the lake is summarized in Table 12. 



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

 different habitats showed that the algal species clearly fall into two 

 main groups. 



(i) Those typical of the inner parts of reed swamps (organic 

 shores). 



