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



in places. I rarely stayed more than two or three days in any one locality, 

 so that although able to familiarise myself with a wide range of climatic 

 conditions and their influence on algal growth, I was unable to enter into 

 detailed study of any given problem. Moreover, my observations, of course, 

 merely deal with one phase of the algal vegetation, and it is possible that 

 many other peculiarities would come to light if the period of observation 

 could be extended over an entire year. I am, however, inclined to think that 

 algal growth in the tropics will not show so marked a periodicity as obtains 

 in our parts. The rice-fields alone are likely to be interesting from this point 

 of view (see p. 242), since the Alga? in them are exposed to regularly 

 alternating periods of desiccation and inundation. The greater part of my 

 observations were carried out during the dry season, although I remained 

 long enough to see some of the effects of the heavy rains, which begin in 

 November. In many respects I was fortunate in being able to collect during 

 the dry period, since the rains would very soon make access to many of the 

 pieces of water studied exceedingly difficult. The dry season is, moreover, 

 the interesting one from our point of view, for we then have a very essential 

 factor influencing tropical algal vegetation in an acute stage, viz., the risk of 

 desiccation under the burning glare of the tropical sun. 



The main purpose of the present paper* is to indicate some of the more 

 important differences between the subaerial and fresh-water algal vegetation 

 occurring in the tropics and that found in temperate regions, and also to point 

 out the essential variations in tropical algal vegetation under the influence of 

 diverse external conditions. Most of those who have written on the subject 

 of algal vegetation in the tropics — and the literature is practically confined to 

 a few short introductory remarks in the systematic floras — have emphasised 

 its similarity to that of temperate regions,*)* and little or no attempt has been 

 made at determining the differences ; this is mainly due to the fact that most 

 of the works on tropical fresh-water Algse are the outcome of casual, and on 

 the whole, probably very unrepresentative collections by botanical travellers 

 whose main interest lay in other directions. No one, as far as I am aware, has 



* A large part of the expenses of the present investigation were covered by a grant 

 from the Government Grant Committee of the Royal Society, to whom I am much 

 indebted for the help thus afforded to me. I also take this opportunity of heartily 

 thanking all those who were kind enough to assist me in the course of these investigations, 

 either by their extensive hospitality or by direct help during the performance of the 

 work. I wish especially to return thanks to Dr. J. C. Willis, Mr. Carruthers, and 

 Mr. Wright, of Peradeniya, to Mr. K. Bamber and Dr. A. Willey, of Colombo, to 

 Mr. Nock, at Hakgalla, and Mr. Lewis, of the Forest Department. The entire illustration 

 of this paper has been carried out by my wife. 



+ Cy., for instance, Lemmermann, " Ub. die v. Herrn Dr. Volz auf seiner Weltreise 

 gesammelten Susswasseralgen," 'Abh. Nat.-Ver.,' Bremen, vol. 18, 1905, p. 143 et seq. 



