1907.] 



Fresh-water Algal Flora of Ceylon. 



225 



where this latter is poorly developed, an exclamation mark in brackets 

 is added. 



At first sight this table may not appear to bear out the above statement of 

 the dominance of the blue-green element very clearly, but a consultation of 

 the map will show that all the large and important tanks and lakes come 

 into the first or second columns, the only noticeable exceptions being 

 Kelawewa and Kurunegalawewa.* I may also point out that of the 

 tanks enumerated in the third column, five (all near Kekirawa) are 

 probably in connection with one another and with the waters of Kelawewa, 

 and that a considerable number of them (five) are very poor in 

 organic life altogether, which cannot be said of any of those in the first 

 column. I have endeavoured to bring out this latter point more clearly by 

 employing heavy type for those tanks which have an abundant algal 

 vegetation (either littoral or pelagic or both). It will be seen that whereas 

 nearly all the tanks with a dominant blue-green vegetation are rich in Algae, 

 this is only the case with respect to two of the tanks in the third column. 

 In further illustration of this point, I append lists of tanks in which the 

 green and blue-green forms respectively are negligible (the same 

 arrangement of type is preserved) : — 



Green Element negligible. 



Basawakkulam. 



Tank in Anuradhapoora Gardens. 



Town Tanks, Anuradhapoora. 



Dambullawewa (Plankton only !). 



Madawachyawewa. 



Neravieawewa. 



Pokuna on top of Sigiri (Plankton only !). 



Lake Kantelai. 



Andankulam. 



Hiriwadunnawewa. 



Blue-green Element negligible. 



Mancadawawewa. 



Punchi kekirawa. 



Tibbotuwawewewa. 



Malawewa. 



Senadiniyagawawewa (Plankton only !). 



Namoluwewa. 



Megaswewa (Plankton only !). 



Wendrenkulam (Plankton only !). 



Kurunegalawewa. 



Borlasgamawewa. 



Mahakadawellawewa. 



As an outcome of these considerations, we may state that whenever there 

 is a well-developed algal flora in the considerable number of Ceylon tanks 

 and lakes I have examined there is always a noticeable blue-green element 

 which very frequently dominates the entire algal growth. If we now attempt 

 a comparison of the features just discussed with those of other tropical 



* It is an interesting point that the dominance of the blue-green element is most 

 pronounced in the larger tanks. The smaller tanks probably present conditions somewhat 

 analogous to those prevailing in the smaller pools and ditches (viz., greater risk of sudden 

 desiccation, and stagnant water with less aeration ; cf. the next section of this chapter). 

 The smaller tanks thus gradually carry us over to the small pieces of water considered 

 subsequently. 



