237 
Algal Flora of the Tropics. 
gleichgiiltig, die genauen zufalligen Standorte solcher Ubiquisten zu 
kennen.’ I think it very unlikely that for many of the forms enumerated 
by him without any mention as to locality that the latter is at all 4 zufallig ’ 
(cf. also below). In view of these facts it is very difficult in most cases 
to obtain the kind of information we want from the tropical floras. I may 
take this opportunity of urging the importance of careful notes on relative 
abundance of species and habitat to all algal collectors, and more particu- 
larly to those who do not work out the results of their own collections, 
but pass them on to specialists for investigation. There is one other 
feature that it is well to pay attention to during the compilation of a flora, 
and that is the usual associates of certain forms to be considered in greater 
detail below. Data of this kind are to be found in a number of algal 
floras, but one completely misses them in others. And yet such data 
are hardly less important in aiding one to call up a picture of the algal 
vegetation of a given district than the relative abundance of the different 
species. 
The subsequent remarks are based on the records contained in the 
literature enumerated at the end of this paper, and are supplemented and 
originally stimulated by observations made in Ceylon. The bibliography 
does not pretend to be absolutely complete, but I think that all the more 
extensive papers are included, and also all the smaller ones containing data 
bearing on the present subject. Only such papers are included as deal 
either entirely or partly with the flora of regions situated between the 
tropics of Cancer and Capricorn. This limitation is of necessity somewhat 
artificial, but I saw no other way of drawing a boundary. 
In the course of the subsequent considerations it has frequently been 
necessary to enumerate all the records of a genus or group of genera. 
I have endeavoured to make these lists as complete and as accurate as 
possible in the hope that they may not only prove of service from the 
point of view of the present paper, but also as an epitome of our present 
knowledge of the distribution of these forms in the tropics. On the whole 
I have, however, refrained from dealing with these records critically, as 
such a treatment would have necessitated a much greater extension of this 
paper than seemed advisable. 
2. The Systematic Composition of the Subaerial Algal 
Flora of the Tropics. 
I have already elsewhere 1 pointed out the very different character of 
the subaerial algal vegetation in the tropics and in our parts of the world. 
The difference not only concerns the relative extent of development, but 
also the specific composition. With reference to the former point, my 
experience is gained from observation in the damp districts of Ceylon, 
1 Proc. Roy. Soc., Ser. B, vol. lxxix, 1907. 
