251 
Algal Flora of the Tropics. 
(Plankton of a fountain-basin near Langenberg) ; ( e ) Schmidle, ’00 a, p. 160 (no 
locality mentioned); (f) Schmidle, ’00 a, p. 160 (var. macromeres (Wittr.), Stockm. ; 
no locality given); (^)Wille, ’ 03 , p. 5, sep. copy (isolated filaments; hot springs, 
Nhaondue; pools near Mutadzi) ; (K) Schmidle, ’97 e, p. 260 (brackish water, Savaii); 
( 7 ) Borge, ’ 06 , p. 4 (at height of 4,000 metres, i.e. cool water; Laguna, Colo- 
rado); (/) Heydrich, ’ 94 , p. 271 (var. Julianum (Menegh.), Rabenh. ; rocks, S. 
Formosa); (h) Schmidle, ’ 95 , p. 296 (var .striatum, Schmidle; probably flowing 
water, West Sumatra); (/) West and West, ’ 99 , p. 281 (var. tortuosum , Stockm.; 
in small stream, Roseau Valley, Dominica) ; (pi) ? Grunow, ’ 67 , p. 37 (freshwater, 
Rio de Janeiro; also var. crassior from Tahiti). 
20. Rhizoclonium spongiosum , Dickie. — (a) Dickie, ' 81 , p. 124 (forming spongy 
masses \ to inch thick on wet sandstone rocks near Manaos, i.e. a terrestrial 
form). 
N.B. — This list does not absolutely exhaust all the records of freshwater species 
of these two genera found in the works enumerated in the bibliography at the end 
of this paper. All those in which a definite habitat was given are included, but 
a certain number of others, which were extremely vague, have been left out. A number 
of the records of Cladophora , published prior to Wittrock’s monograph of the 
Pithophoraceae (in Nova Acta Reg. Soc. Sc. Upsala., Ser. 3, 1876 ), really refer to 
species of Pithophora (cf. loc. cit„ pp. 2 and 3) — possibly even some of the later 
ones, although Pithophora is on the whole quite easily distinguished from Cladophora , 
even in the sterile condition, by its habit and its mode of branching (loc. cit., p. 4). 
Where details as to habitat are given, the important feature from the present 
point of view is indicated by the use of black type. 
I think it is scarcely necessary to make much further comment on this 
list. It shows that in a large number of cases the individuals of these two 
genera were found in flowing water or in water which was better aerated 
than the ordinary freshwaters of the tropics are. The remaining cases 
cannot be taken as a decisive proof to the contrary until such habitats 
have been fully studied. Moreover, as in the majority of cases there is 
absolutely no mention of the amount of the Alga, we do not know whether 
we are dealing with an abundant form or merely with an isolated occur- 
rence. A number of the localities, which do not obviously point to well- 
aerated water, are very suggestive of artificial aeration (e. g. that inhabited 
by Messrs. West and Wests Cladophora incur vat a 1 ). 
It will have been gathered from the preceding remarks that I am 
attempting to show that Cladophora and Rhizoclonium are relatively so 
scarce in tropical freshwaters, because the ordinary waters are too poorly 
aerated to admit of their existence. Owing to their higher temperature 
tropical waters contain a far smaller amount of the essential gases 
(oxygen and carbon dioxide) than do those of temperate regions. In 
1 I unfortunately omitted to visit this locality during my stay in Ceylon. 
T 
