236 
Fritsch. — The Subaerial and Freshwater 
are, therefore, subject to much the same conditions in all parts of our 
globe 1 . But in spite of this uniformity of conditions, which is too obvious 
to need further comment, there are considerable minor diversities, which 
have been overlooked or not adequately considered, and no attempt has 
been made to correlate them with any peculiarity of the algal growth in 
different regions. Moreover, as regards the subaerial algal vegetation the 
influencing factors are markedly different in the tropics to those existing 
in our parts of the world, and here we have a much more fundamental 
and obvious difference in character. It is my object in the present paper 
to attempt an analysis of the existing data on tropical freshwater and 
subaerial Algae with the help of certain observations made in Ceylon. 
I hope to be able to show that the apparent similarity of algal growth 
all over the world is not quite as great as is generally imagined. 
Very few of the existing tropical algal floras can be regarded as in 
any way representative of the region they deal with. Many of them are 
merely records of the occurrence of a few species in a certain district, and 
even the more extensive ones show marked signs of being incomplete in 
one direction or other. They are nearly all the result of casual collections 
made by botanical travellers occupied in the investigation of other 
problems, and the only exceptions are those of Welwitsch, Hansgirg, and 
De Wildeman. The two latter are, as far as I am aware, the only 
algologists who have had opportunities of collecting in person in the 
tropics, and even they were occupied with other investigations at the same 
time, and did not devote their whole attention to the algal flora. None 
of the existing floras aim at giving a true picture of the algal vegetation. 
They, of course, give us a record of a larger or smaller number of algal 
species found in a certain district, but they tell us nothing about the 
relative abundance in individuals of these species. The specific lists are 
of little use from this point of view, for, although a flora may include only 
a small specific element of a certain group, the number of individuals may 
be very great, and the group may play a very important part in the algal 
vegetation. Little blame attaches to the specialists who have worked out 
the collections, but one cannot suppress a certain amount of disappointment 
at the remissness of the collectors themselves in this respect. And this is 
not the only criticism that they call forth, for one misses in most of the 
floras adequate data as to locality and habitat, without which a flora 
becomes practically useless except from the geographical point of view. 
In very many cases the only information as to locality given is furnished 
by a mention of some province or town. Even some of the algologists 
do not appear to realize the necessity of as complete data as possible on 
these points (Turner, ’92). I cannot in the very least agree with Schmidle 
(’00 A, p. 160 ) when he says: c Es ist doch fur die Wissenschaft vollig 
1 Cf. also Lemmermann, ’ 06 , p. 144 et seq. 
