1907.] Fresh-water Algal Flora of Ceylon. 247 



members of the Protococcales (Scenedesmus, Pediastrum, Ccelastrum, 

 Bhaphidimn, Dimorphococcus, etc.) sometimes accompany the Conjugate 

 element in striking numbers, and in one or two cases Peridiniacese are quite 

 common. The exceptional abundance of the flora in these rock-pools can 

 only be referred to the high temperature of the water (perhaps also to the 

 favourable conditions of aeration ?).* 



Before concluding the description of the algal vegetation in the rock-pools, 

 I wish to add a few remarks on the biology of the attached growth found on 

 the rocky sides of these pools, and we may extend the discussion to the algal 

 covering on submerged rock-surfaces in general. This attached growth is 

 either an adhesive tangle or is composed of velvety tufts of pilse. The former 

 is often very compact, and consists either of a single species or more commonly 

 of a number of closely interwoven forms. The basis in the latter case is 

 generally blue-green, although green forms (CEdogonium, Mougeotia, Microspore?,, 

 Vlothrix, Stigeoclonium) often make up a large part of the mass, whilst 

 unicellular forms (Desmids, Diatoms, Protococcales) are frequently inter- 

 mingled. Such adhesive tangles are, no doubt, composed of certain definite 

 associations of species mutually dependent one upon another in certain 

 respects, and extensive investigation would probably show that similar (in 

 some cases perhaps identical) collections of species occur in different localities 

 under the same influencing conditions. The advantage of such composite 

 growth may lie in its forming a source of protection against the ravages of 

 aquatic animals, but there may even be a more intimate relation involving 

 the metabolic activities of the organisms concerned. For such associations of 

 species I propose the term " consortium"^ one example of which has already 

 been noticed in the Zyngbya-films found in Lakes Kantelai and Mineri 

 (p. 227) ; Pithophora, with its associated epiphytes, may be mentioned as a 

 secondj Consortia are, of course, to be found in every piece of water, and I 

 hope at some later date to deal with those occurring in our waters. 



* It may be suggested that the great specific diversity and relative individual 

 complexity presented by the algal flora in these pools (and especially in the deeper ones) 

 may be, to some extent, due to an absence of the external conditions influencing algal 

 growth in other tropical pieces of water. Especially in deep rock-pools desiccation 

 probably never takes place ; the temperature is not subject to much daily variation ; the 

 aeration is probably fairly adequate ; and the light conditions are not extreme. These 

 characters of the habitat are probably favourable to the growth of a large number of 

 different forms, whose vegetation goes on undisturbedly. A considerable amount of 

 variation is thus possible in these waters, and I should not be surprised if a relatively 

 large number of new forms will be found in them as a result of a more extensive 

 investigation. 



t Consortium (Latin) = fellowship, participation. 



X Cf. Fritsch, "Problems in Aquatic Biology, etc.," ' New Phytol.,' vol. 5, No. 7, 1906, 



