254 On the Subaerial and Fresh-water Algal Flora of Ceylon. 



{e.g., the occurrence of Micrasterias foliacea, one of the few forms of this 

 genus that has assumed the filamentous condition). It is, of course, quite 

 possible that there are other more obscure causes for the great scarcity of 

 filamentous Desmids in the upland pools. With reference to the above 

 suggestion, it may be pointed out that filamentous Desmids are, on the 

 whole, also a rather rare feature in our waters (except Hyalotheca dissiliens 

 (Sm.), Breb., and Gymnozyga moniliformis, Ehrenk), which may be due to the 

 higher percentage of dissolved oxygen. 



Of the unicellular Desmids, Cosmarium, Uuastrum, and Glosterium play 

 the most important part in the composition of the films, one of these three 

 being generally the dominant form. In some cases one or other of these 

 three genera is almost alone represented, and we obtain a practically pure 

 culture of a number of species of the respective genus. In other cases, 

 however, the films show a more varied aspect, containing most of the Desmid 

 genera above mentioned, though many of them only occur in subordinate 

 amount. Some of the films are composed of Desmids only ; in others various 

 Protococcales (Baphidium, Crucigenia, Ccelastrum, Uremosphcera, Scenedesmus, 

 etc.) play a more or less important part. No doubt the presence or absence 

 of these latter forms depends on certain conditions — possibly on the quantity 

 of organic substance dissolved in the water.* Diatoms occasionally occur 

 in some quantity, but are often almost completely wanting. 



The algal vegetation in the small pools of the uplands does not, however, 

 always take the form of these films. In some cases one finds a granular or 

 flocculose covering on the bottom, whose composition is quite identical to that 

 of the films. A mass of filamentous green Algse floating on the surface 

 (Spirogyra, Mougeotia, Ulothrix, frequently associated with Desmids) is not 

 very common. In a few cases various blue-green Algae are found, mostly 

 as a fluffy coating to weeds, etc. I was unable to determine whether they 

 are only developed in particularly exposed localities. Lastly, I may mention 

 that I met with a species of Vaucheria in the water of a small pool in the 

 Hakgalla Botanic Gardens. This is the first record of a fresh-water species 

 of Vaucheria from Ceylon. 



Meagre as the facts thus are that I was able to derive from my brief 

 study of the vegetation of these upland pools, they yet point to a marked 

 diversity as compared with the lowlands and a distinct similarity to the 

 algal flora of temperate regions. These facts point to the temperature of 

 the water (and indirectly the lower percentage of dissolved oxygen) as one 

 of the chief factors influencing tropical algal vegetation. 



* Cf. Schmidle, " Aus der Chlorophyceen-Flora der Torfstiche zu Virnheim," ' Flora,' 

 vol. 78, 1894, p. 64. 



