40 
Tansley and Fritsch. 
varying and often predominating amount of filamentous blue-green 
forms are associated ( Lyngbya ,). In some localities ( e.g. Bentotta) 
the pneumatophores of Sonneratia are covered with a fairly dense 
growth of (apparently) the same red forms as occur on the 
Rliizopliora- roots, whilst in other localities {e.g. Kalutara) a careful 
examination revealed no traces of Algae on the Sonneratia. It 
should be pointed out that the red forms are practically confined to 
the root-structures of these two plants. Small quantities of them 
were found in other situations (e.g. stone-work of landing-stage at 
Negombo, rocks near railway-bridge in river at Bentotta), but these 
were merely isolated occurrences. It seems probable that these 
forms are adapted to live on the peculiar spongy substratum 
afforded by the bark of the roots of Rliizopliora and Sonneratia. 
As far as our observations go they become rarer as one moves 
away from the sea. It should be added that similar red Algae 
have been described by Schimper 1 and Goebel 2 for the American 
mangroves and by the former also for the Indian mangroves, but a 
careful investigation is much needed. 
The roots of Acanthus ilicifolius and also some of its horizontal 
branches which dip into the water, afford a rather different 
substratum; this is evidently quite unsuitable for the above- 
mentioned Rhodophyceae, which are never to be found on them, 
although Acanthus often grows in the immediate vicinity of 
Rliizopliora or Sonneratia bearing the red forms. The submerged 
portions of the Acanthus however almost invariably have a thin algal 
covering of another kind, composed of filamentous Cyanophyceae 
of the Rivularia- group . 3 
4.—Semi-Mangrove or Semi-Halophyte Vegetation (including 
Nipa- formation of Schimper). 4 
All the species hitherto mentioned may be said to belong to the 
mangrove-formation proper, since they all shew definite adap¬ 
tations, in their root-systems, and often also in their habit of 
1 Schimper, Indo-Malay. Strandflora. 1891. p. 65 ; Pflanzen- 
geographie. 1898. p. 827. 
2 Goebel, Ueb. einige Siisswasserfloridecn aus Britisch-Guyana. 
Flora. Vol. 83. 1897. p. 436. 
3 The Algae of the mangrove-formation will subsequently be 
described in much greater detail by one of us. 
4 In the course of a further examination of the evidence before 
us we have decided to depart from Schimper’s classification 
given on p. 3. Cf. below and especially our table on pp. 50, 51, 
where the relation between the semi-mangroves and the true 
mangroves is shown. 
