Algal Flora of the Tropics . 
269 
Summary. 
The more important conclusions or suggestions brought forward in the 
present paper may be briefly summarized as follows : — 
(i) There is some evidence to show that in the damp tropics there 
is always a very extensive subaerial algal covering, equal to or perhaps 
even surpassing that examined by the author in Ceylon. 
(ii) The subaerial algal growth in Ceylon consists almost entirely 
of Cyanophyceae, and there is evidence in the literature that in other parts 
of the tropics this group is equally predominant in the subaerial algal flora. 
There are not very many records of green subaerial forms in the literature 
(see however iv), and it is probable that they play a very small part in the 
tropics. 
(iii) The Cyanophyceae are probably an essentially tropical group, 
and it is not impossible that they may be the descendants of primitive algal 
forms, which existed in earlier periods under conditions analogous to those 
found in the damp tropics at the present day. 
(iv) Trentepohlia is the only genus of green Algae that is really 
successful in the subaerial flora (apart from other members of the Chroole- 
pideae, which have become epiphyllous, and from the parasitic genera 
Phyllo siphon and Phytophysal) 
(v) In the submerged algal flora of tropical freshwaters the Cyano- 
phyceae also constitute a very important element, though not as preponderant 
as in the subaerial flora. They are equally important in the Plankton. 
(vi) The freshwater algal flora of the tropics is composed of forms in 
which narrow filaments are much more abundant than broad ones, a fact 
which is brought into relation with the small amount of dissolved oxygen 
in the water. Exceptions are constituted by Pithophora and Spirogyra , 
especially by the latter. 
(vii) Cladophora and Rhizoclonium are very poorly represented in 
tropical freshwaters in comparison to their abundant occurrence in our parts, 
and there is good evidence to show that in most cases they favour well- 
aerated (e. g. running) water. The chief representative of Cladophoraceae 
in the tropics is Pithophora , which appears to be an essentially tropical 
genus. 
(viii) Vaucheria is very rare in the tropics. This refers especially to 
the aquatic species, but the terrestrial ones are not much commoner. 
Botrydium is equally rare. It is possible that the peculiar assimilatory 
process in these two forms is responsible (the same applies to the Confervales). 
(ix) The Confervales are not very well represented, the most abundant 
form being Ophiocytium . Conferva is not well represented, and tends to be 
restricted to well-aerated water. 
(x) In the case of the Ulotrichales it is not quite evident at present 
