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



must look upon the higher temperature (only 4° C. above the other, however) 

 as being the cause of the absence of Fragilaria in the hotter springs. 



(vi) Algal Vegetation in the Small Pools of the Uplands. — The vegetation of 

 the numerous small pools occurring round about Nuwara Eliya (especially 

 on the so-called Moon Plains and along the route from Nuwara Eliya to 

 Hakgalla) formed a ready means of study and furnished interesting materials 

 for a comparison with the lowland pools. The differences are just what we 

 should expect to find in view of the different conditions. As Mr. Nock kindly 

 informed me, these small upland pools dry up for about a month during the 

 dry period. Their water is generally almost quite clear, but stagnant, and the 

 midday temperature (October 29) in four cases was found to be 19°*5 C. The 

 bottom and sides in some cases seemed to consist of a white sandy loam, but in 

 other cases they were clayey. Some of the pools are of considerable depth, 

 others, again, shallow. Except for the slight shade afforded by the growth of 

 neighbouring grasses, etc., the only protection from the strong light is found 

 in the frequent occurrence of water-weeds, but some of the pools are quite 

 destitute of such growth. The important conditions are the fairly low 

 temperature, the clear water, and the probably rather intense illumination. 



In very many of the pools the algal vegetation takes the form of a thin, 

 almost transparent filmy growth covering the abundant water- weeds, and 

 occasionally floating on the surface of the water. These films are so delicate 

 that they break up as soon as one attempts to remove the weeds bearing them 

 from the water, and the only way to collect them is to push the plants into the 

 collecting-tube under water. This character of the films is due to their being 

 composed almost entirely of unicellular forms, of which Desmids and a limited 

 number of Protococcales are the most important. Algal growth of this kind 

 is common enough in temperate regions,* and it is interesting to find it 

 developed here, in this pseudo-temperate part of Ceylon ; as far as I have 

 seen, such films are not present in the lowland waters. A considerable part 

 of the films is composed of mud and decaying organic particles, and this 

 matter and the algal cells are no doubt held together to form a coherent whole 

 by the considerable masses of mucilagef excreted by the Algae forming the 

 films. This mucilage is, however, very delicate, in most cases not being 

 obvious without the help of stains, and this accounts for the very deli- 

 cate and frangible nature of the films. Although films of this type have 

 frequently been described, their origin has, as far as I am aware, not yet been 



* Cf. Messrs. West and West, " A Monograph of the British Desinidiaceae," vol. 1, Eay 

 Society, 1904, p. 16. 



t See especially B. Schroder, " Untersuchungen iiber Gallertbildungen der Algen," 

 < Verh. Nat.-Med. Ver., 5 Heidelberg N. F., vol. 7, 1902, pp. 139—196, Plates VI and VII. 



