2 54 
Fritsch . — The Subaerial and Freshwater 
In minor numbers they are generally present in every collection, although 
certain types of waters are practically destitute of them. 
From what I have seen in Ceylon it seems as though the epiphytic 
Diatoms of tropical waters were not in general quite the same as those 
found in our parts of the world. The species of Cocconeis in particular 
are very rare, whilst Achnanthes seems to play a very much more important 
part than with us. Most of the tropical floras, however, give us little or 
no information about Diatoms 1 , and I prefer, therefore, to omit further 
speculation on this subject until more data are available for general 
verification. In the case of abundant occurrence of tropical freshwater 
Diatoms it is also of course of the utmost importance to have full descrip- 
tions of the habitats. It seems as though the small amount of dissolved 
gases in the water may again be the governing factor in determining the 
scarcity of this group in stagnant tropical waters. 
(ii) The Freshwater and Terrestrial Siphoneae of 
the Tropics. 
The genus Vaucheria is quite evidently very poorly represented in the 
tropics. In the case of Ceylon I have not as yet found a single example 
of its occurrence in the lowlands, although (in the course of a six days’ stay 
only) in the uplands, at a height of 6,000 feet and more, both aquatic and 
terrestrial forms were met with. The literature is equally poor in records 
of this genus; the following are extracted from the papers in the 
bibliography : — 
1. Vaucheria geminata (Vauch.),DC. — (a) Hieronymus, ’ 95 , p. 23 (in ditches, &c.). 
2. Vaucheria humicola , Lagerh. — (a) Lagerheim, ’ 90 , p. 14 (in terra humida 
horti botanici Quitensis 2 ). 
3. Vaucheria repens (Hass.), Klebs. — (a) Schmidle, ’02 a, p. 64 (forma nasuta , 
Schmidle ; on damp stones in streamlet Njasoso and on damp soil on the banks ; 
Africa). 
4. Vaucheria sessilis (Vauch.), DC. — ( a ) West and West , ’97 a, p. 235 (Golungo 
Alto 2 , Africa. In fossis exsiccatis adhuc humidis in Varzea pone dom. Isidni; 
covers in Aug. and Sept, all the half-dried-up ditches of the plain) ; (b) West and 
West, ’97 a, p. 235 (var. monogyna , W. and G. S. West; Golungo Alto 2 , Africa. Ad 
margines stagnorum rivi Cuango, Aug. 1857) ; ( c ) Zeller, ’ 73 , p. 186 (var. cespi/osa Ag. ; 
Pegu, Yoma centralis, Khayeng-mathay-choung, Burma. Var. repens , Hass., ibidem, 
in limo siccescente) ; ( d ) Zeller, ’ 76 , p. 427 (var. subarticulata , Zeller; no locality). 
Sterile species of Vaucheria are recorded by (a) Dickie, ’ 81 , p. 125 (on moist 
earth, Porto Salvo, Rio Purus) ; (b) Schmidle, ’03 a, p. 86 (Plankton of Nyassa, near 
Langenburg !); (r) De Toni, ’ 92 , p. 272 (in rivulis, inter Gheleb et Maigerghebit) ; 
(d) Turner, ’ 92 , p. 155 (in fragmentary condition only; Bengal, Central India!); 
1 Cf., however, De Wildeman (’00), West and West (’02 b), Lemrnermann (’05 and ’06), 
Gutwinski and Chmielewski (’06), Dickie (’81). 
2 These localities are situated at a high altitude. 
