344 FRESH-WATER ECOLOGY I 



A very definite gradation or succession can be traced in the algal 

 flora as one passes from the inner to the outer reed swamps, from 

 the latter to the open water or stony inorganic shores and finally 



Table XVII 



No. of 



species 



A. Occurrence of species 

 (i) Species present throughout the year with no distinguishable 4 



maximum 



(2) Species present throughout the year with a maximum at one 4 

 period 



(3) Species present in abundance only at certain times of the 7 

 year 



(4) Species present in some degree at certain times of the year Numerous 



B. Occurrence of maximum 

 (i) Species with a spring maximum and smaller autumn maxi- 9 



mum; diatoms predominant 



(2) Species with a spring maximum only 3 



(3) Species with a summer maximum only; Chlorophyceae 11 

 predominate 



(4) Species with an autumn maximum only; Cyanophyceae 11 

 predominate 



(5) Species with a winter maximum only; Chlorophyceae 7 

 predominate 



C. Time of year when different species occur in abundance at their 

 greatest depth 

 (i) Species attaining greatest depth in spring; diatoms only 3 



(2) Species attaining greatest depth in spring and autumn 3 



(3) Species attaining greatest depth in summer; Chlorophyceae 10 

 predominate 



(4) Species attaining greatest depth in autumn i 



N03 



(a) Stony and Moderately 



rocky shores high 

 (inorganic) 



(b) Mouths of High 



streams 



(c) Reed swamps Low 



(organic) high 



to the mouth of streams. In other words a progressive change in 

 the algal flora is associated with a bottom that becomes less 

 and less organic in nature or as one passes from eutrophic to 

 oligo trophic conditions. 



