2 43 
Algal Flora of the Tropics . 
walls, &c., but has also stimulated an epiphyllous tendency in many of the 
subaerial forms. Apart from epiphyllous Lichens and Liverworts, of the 
existence of which probably every one is familiar, we find a number of blue- 
green and green forms growing on the leaves of the higher tropical vegetation 
(cf. especially Schmidle, ’97 C, ’97 D, ’97 F, and ’98 B; Mobius, ’88; Raciborski, 
’00). The blue-green forms are in great part the same as are met with 
in the general subaerial growth, and it is easy to comprehend how they 
invade moisture-covered leaves from neighbouring subaerial habitats. This 
phenomenon can be readily observed in the Nepenthes- house at Kew, where 
diverse blue-green forms settle down on the leaves of the plants cultivated 
there. The green forms, however, which have acquired the epiphyllous 
habit are on the whole much more specialized. They are all members of 
the Chroolepideae, the chief genera being Cephaleuros , Mycoidea , Phycopeltis , 
Pkyllactidium, and Phylloplax (literature — Cunningham, ’80; De Toni and 
Saccardo, ’90; De Wildeman, ’00; Karsten, ’91 ; Mobius, ’88 ; Raciborski, ’00; 
Schmidle, ’97 C, ’98 B, ’99 ; Ward, ’84). Their structure is adapted to their 
mode of life, and like the species of Trentepohlia , their cells contain a 
yellow or red colouring matter, which exerts a screening action on the 
chlorophyll. The genera Phyllosiphon. and Phytophysa (see especially De 
Wildeman, ’00 ; Lagerheim, ’92 ; and Raciborski, ’00) have gone still 
further, since they penetrate the tissues of their substratum and lead a 
parasitic life. These diverse cases are of the utmost interest as showing 
the range of possibilities afforded by life in tropical subaerial habitats. 
3. The Systematic Composition of the Submerged Aquatic 
Algal Flora of the Tropics. 
A careful study of the freshwater algal flora of the tropics, such as I 
was able to undertake in Ceylon, brings out two points, viz. : (a) the 
dominance of the blue-green group, especially in the larger pieces of water, 
and (b) certain peculiarities of the green algal vegetation when considered 
as a whole. In dealing with the general characters presented by the 
submerged algal growth of the numerous (often large) freshwater tanks of 
Ceylon, I summarized my observations by stating 1 that s whenever there 
is a well-developed algal flora in the considerable number of Ceylon tanks 
and lakes I have examined, there is always a noticeable blue-green element 
which very frequently dominates the entire algal growth l The observations 
on which these conclusions are based are given in some detail in my paper 
on the general character of the freshwater algal flora of Ceylon (Fritsch, loc. 
cit), and it will be sufficient to mention that of 46 tanks investigated 18 
were absolutely dominated by Cyanophyceae with practically no green algal 
growth, while of the remainder 16 contained quite a considerable mass of 
1 loc. cit. 
