263 
Algal Flora of the Tropics. 
be found to have a fairly wide range. It is noticeable that, although the 
algal flora has received considerable attention, only sterile Spirogyras have 
as yet been recorded from the Sandwich Islands. There are no records at 
all in Volken’s algal collections from the Carolines, although they are so 
scanty that not much weight can be attached to this point (Schmidle, ’01 B). 
Schmidle (’97 b) does not record any Spirogyras from the tropical parts of 
Polynesia, but from the Samoa Islands (Schmidle, ’97 E) sterile species 
again are known. The literature offers too few data as to habitat 
to enable one to say anything of general application on this subject. In 
Ceylon, Spirogyra was found most abundantly in smaller, absolutely 
stagnant pieces of water (small ditches, rice-fields, &c.), and generally 
occurred in localities where it was more or less shaded either by a dense 
growth of aquatic Phanerogams or by the surrounding terrestrial vegetation. 
So little is known about the significance of the infolded transverse walls 
found in many of the narrower species of Spirogyra that we are not 
in a position to understand the reasons for the scarcity of species exhibiting 
this phenomenon in tropical waters. The infolding is usually looked upon 
as a mechanism for the disjunction of the cells of a filament, but from this 
point of view its scarcity in the tropics is inexplicable. Since it is mostly 
found in quite narrow forms, the rarity of these latter may be responsible, 
although that does not seem very likely. 
In comparison to Spirogyra the other genera of Zygnemaceae play 
a very small part in the tropics ; that is, however, the same relation as 
obtains in our flora. There are records of a considerable number of species 
of Mougeotia and Zygnema (inch Zygogonium ), also Gonatonema (G. tro - 
picum , W. and G. S. West) and Sirogonium (S. sticticum , Kutz.). All these 
four genera have also been met with in Ceylon. In addition to this we have 
the two monotypic genera Temnogametum , W. and G. S. West, and Pyxispora , 
W. and G. S. West, from Africa (West and West, ’97 a). Debarya , Wittr., 
has not yet been recorded from the tropics. 
(vi) The Desmids of the Tropics. 
Diverse as the Desmid-flora of temperate waters is, it appears to be 
excelled in the tropics. There is quite an extensive literature dealing with 
floristic records of tropical Desmids, and I must refer to the same for details 
on this point. One cannot say that a group so abundant in our flora finds 
more favourable conditions of existence in the tropics, but it does appear 
that along certain lines evolution of form in the Desmids has surpassed 
itself in tropical waters. 
The only object I have in view here in dealing with tropical Desmids 
is to point out the important part which filamentous forms play. In our 
flora filamentous Desmids are distinctly rare, Hyalotheca dissiliens , Breb., 
and Gymnozyga moniliformis , Ehrenb., perhaps being the two commonest. 
