236 Dr. F. E. Fritsch. On the Subaerial and [Jan. 2, 



It is interesting that if the latter genus is entirely wanting CyanophyceaB 

 generally take the lead (cf. the remarks in the preceding paragraph). 

 Desmids are occasionally very abundant, whilst other unicellular and 

 colonial green forms (Protococcales, etc.) are rare in these lowland waters ; 

 colonial Cyanophyeeae (e.g., Merismopedia, Gomphosphceria) are sometimes not 

 uncommon. In comparison with temperate regions the scarcity of Diatoms 

 is very noticeable, which is not difficult of explanation when one recollects 

 that these forms have a preference for cold water, and even in our parts 

 generally attain their maximum during the winter months. Yet both. 

 Diatoms and Desmids are a good deal commoner in the pools and ditches 

 than in the tanks. 



The large majority of these pools and ditches of the lowlands are 

 characterised by a Spirogyra-CEdogonium* vegetation, the latter genus, though 

 relatively rarely attaining abundant development, being almost invariably 

 present in some quantity. This vegetation acquires different aspects accord- 

 ing to the subsidiary forms present and is particularly well emphasised in 

 certain pools and ditches owing to the almost constant association of other 

 species with the Spirogyra and CEdogonium. 



The pools and ditches thus characterised always exhibit a dense, brownish- 

 red granular deposit on the bottom, and the same deposit often also con- 

 stitutes a filmy investment to all the water-plants. This deposit consists of 

 ferric hydroxide, and I will consequently talk of these pieces of water as 

 ferruginous pools.f Such pools are very common in all the lowland regions 

 with a considerable rainfall (e.g., Negombo, Colombo, Hanwella, etc.), and are 

 not rare in the uplands around Nuwara Eliya. Owing to the uniform 

 character of the algal flora, these ferruginous pools may all be considered 

 together (i.e., both those of the lowlands and uplands). In a dozen typical 

 cases examined from different parts of the island, neither Spirogyra nor 

 CEdogonium were ever found to be absent from the pools, although the 

 one or the other (very rarely both) was occasionally only present in small 

 quantity. Of other filamentous forms, various species of Bulbochcete 

 (including B. minuta, West and West, B. spirogranulata, West and West, 

 etc.) are rarely wanting, and may be regarded as a constituent of almost 

 equal importance to the two genera previously mentioned ; they invariably 

 occur as epiphytes on larger water-weeds, and possibly their absence in 

 some few cases is the result of the lack of a suitable substratum. Ulothrix, 



* The species of CEdogonium found in these pieces of water are again prevalently 

 narrow (see p. 232). 



t Similar deposits are also found in the rice-fields, and these waters show the same 

 characteristic flora as that now to be described. 



