1907.] Fresh-water Algal Flora of Ceylon. 201 



attempted to study the subject from the point of view put forward in the 

 present communication.* My object is thus to outline the general features of 

 distribution and biology, and I have rarely spent much time on specific 

 determinations. They would in most cases be quite valueless from the present 

 point of view, and would, moreover, have very considerably delayed publication ; 

 and it seemed well to write this general paper before one's recollections and 

 impressions of the aspect of the algal flora had become dimmed by the lapse 

 of a longer period than has already passed since the work was undertaken. 

 Certain subjects, which are dealt with quite briefly in the present 

 communication, will be considered more fully later on. I hope ultimately to 

 be able to publish a complete systematic list of the Alga3 present in my 

 Ceylon collections, although I prefer to postpone such a publication until 

 I have had opportunities of further study of tropical algal floras. 



Consideration of the Algal Flora. 



The following special considerations are subdivided as follows : — 



(<z) Subaerial Algae, i.e., those growing on trees, stones, walls, etc. (character 



and distribution dependent mainly on temperature, moisture and degree of 



shading) : — 



(i) The lowland vegetation (p. 203). 



(ii) The upland vegetation (p. 215). 



(b) Algal vegetation of the inland fresh-waters (character and distribution 

 dependent mainly on temperature, aeration and composition of water) : — 



(i) Algae of the tanks and other large inland masses of fresh- water 

 (p. 218). 



(ii) Algae of roadside ditches and pools in the lowlands (p. 233). 

 (iii) Algae of marshes and padi-fielcls (p. 241). 

 (iv) Algse of rock-pools (p. 242). 



(v) Algse of wells and springs, i.e., aerated, but standing water (p. 250). 

 (vi) Alga3 of the small pools of the uplands (p. 252).f 



This subdivision is in great part artificial, but it will be found that the 

 character of the algal growth in many of the collections of water mentioned is 

 on the whole sufficiently different to make such a separation useful. It must, 

 however, be pointed out, that in the case of Algae the delimitation of distinct 



* Bohlin, in his l Etude sur la flore algologique d'eau douce des A cores,' gives a some- 

 what analogous account of the algal flora of the subtropical Azores. 



t The second part of this paper, which I hope to publish in the course of the year, will 

 deal with the Algse of flowing water (rivers), and of the lagoons and river-estuaries, and 

 with the Plankton. 



