1907.] Fresh-water Algal Flora of Ceylon. 205 



lowlands of Ceylon with the drier regions having a lower rainfall. Thus at 

 Matara, on the south coast, and at Dambulla, in the Central Province, the 

 decrease in the extent of the algal covering is very marked ; whilst in still 

 drier localities {e.g., Hambantota and Negombo, on the coast, Anuradhapoora, 

 in the North Central Province), houses, rocks, etc., are practically clear of 

 any growth (or only bear small Mosses and Lichens), except in particularly 

 favourable positions. On the other hand, the heavier the rainfall at any 

 locality, under the same conditions of temperature, the more abundantly is 

 the blue-green element developed; the best example of this that I met 

 with was at Labugama (166 inches), where every available object is clothed 

 with blue-green forms. The importance of moisture is also well illustrated in 

 the colonisation of rugged vertical surfaces, since at first only the projections, 

 which are the points about which moisture mainly collects, become occupied 

 by Cyanophyceous growth. 



The importance of a high temperature is also easily recognised. A visit to 

 a wet greenhouse in our regions, which is kept at a relatively low tempera- 

 ture, shows us that here green Algse and Mosses are the more successful 

 elements in the subaerial vegetation, whilst the Cyanophycese, where 

 developed, present a different aspect ; compare, for instance, the growth in the 

 Temperate and Tropical Fern Houses at Kew. The same observation can, in 

 some respects, be made in Ceylon, as we go higher and higher up the central 

 mountain range to Kuwara Eliya (see the discussion of the subaerial Algse of 

 the uplands). 



Though temperature and moisture are in all probability the determining 

 factors in the distribution of the subaerial Cyanophycese within the tropics, 

 this group is provided with certain biological features, which must be 

 regarded as peculiarly suited to the dominant factors of the environment, 

 and enable it to exist so well under the prevailing conditions. In the first 

 place there is a well-marked alternation of a wet and dry period,* which the 

 Cyanophycese are well adapted to withstand, owing to the strongly developed 

 mucilage investments, which are so prominent a feature of the group, and 

 which enable them to withstand prolonged drought.! In this relation, it is 

 interesting to notice that forms with a sheath of semi-liquid diffluent 



* See J. C. Willis, " The Eoyal Botanic Gardens of Ceylon as a Centre for Botanical 

 Study and Kesearch," 'Annals. Boy. Bot. Gards., Peradeniya,' vol. 1, 1901, p. 17 et seq. ; 

 also "Studies in the Morphology and Ecology of the Podostemaceae,'7oc. cit., vol. 1, Part 4, 

 1902, pp. 278—279. 



t Hansgirg, " Ueber Bacillus muralis, Tomaschek, nebst Beitragen zur Kenntnis der 

 Gallertbildungen einiger Spaltalgen," 'Bot. Centralbl., 5 vol. 35, 1888, pp. 54, 102; 

 B. Schroder, " Untersuchungen iiber Gallertbildungen der Algen," ' Verhandl. Nat.-Med. 

 Ver. Heidelberg,' New Ser., vol. 7, p. 183 et seq., especially p. 185. 



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