OP CEYLON AND INDIA. 
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before the branching begins. One arm of the two thus 
formed usually grows much more rapidly than the other. 
At the next branching this is repeated on the other side, 
and so on. The shorter branch of the two, as a rule, does 
not grow out very far, and often remains very short, as in 
the portion of a young plant figured in PL XYI., fig. 6, 
where two of the three branches shown have simply formed 
short projections, fastened to the rock in the usual way. 
The similarity of this figure to that of the alga Bostrychia 
Moritziana as figured by Goebel (Flora, 83, 1897, p. 436) is 
of the most striking description. The alga, it is worth 
noting here, and the subject will be considered again below, 
occurs in the same place with Oenone Imthurni, one of the 
Podostemaceæ of British Guiana. The frequently recurring 
similarity of the Podostemaceæ with the Algæ of moving 
water can scarcely be altogether “accidental.” 
When one of the lateral branches thus formed branches 
again, the first secondary branch is always upon the 
basiscopic side of the primary. The thallus becomes more 
or less zigzag in its construction, the two branches diverging 
at every node. In transverse section (PL XVI., fig. 7) it 
shows an almost cylindrical shape, fiattened on the lower 
side, upon which is a kind of continuous foot, formed by 
the mass of root-hairs or rhizoids. In the central portion, 
but a little towards the lower side, is a vascular bundle of 
very simple construction, described by Warming, who 
states that there are sometimes two xylem groups towards 
the lower side, characterized by spiral vessels. 
Leafy secondary shoots are also developed upon the 
thallus, and soon form, as in Tristicha, the most important 
part of the plant. One shoot forms at each branching of the 
thallus. PL XYI., fig. 3, shows the first leafy shoot appearing 
very early in the life of the thallus, and fig. 4 shows it more 
clearly, with its endogenous origin. The first leaf that 
breaks through is usually towards the basiscopic side, as 
there shown, and the other leaves follow in distichous order. 
The first leaves are small, but the shoot grows rapidly, and 
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