OF CEYLON AND INDIA. 
339 
side of the line of dehiscence. The septa of the fruit break 
away, and the dehiscence ribs split down the middle. As 
in the preceding species, one valve of the fruit falls away, 
the other persisting with its ribs decurrent into the 
pedicel. 
The genus Podostemon, from a morpho-ecological stand- 
point, evidently falls into line with Tristicha, and it will be 
of interest to consider its peculiarities as compared with that 
genus, in connection with the difference in the general 
conditions of life. On the whole, so far as can be judged, 
Podostemon lives in very similar localities to those inhabited 
by Tristicha, but the water is perhaps a little swifter. 
Exposure to light, &c., and the other conditions considered 
in the introduction seem much the same for both. Morpho- 
logically, the chief feature in which Podostemon differs from 
Tristicha is the great reduction of the secondary (and 
probably the primary) shoots. The thallus is very similar, 
though the root-cap is almost absent (as perhaps in Tristicha 
hypnoides), and it is exogenously branched. The secondary 
shoots, however, are much dwarfed, making up for the 
reduction of the axis by the development of very large and 
flexible leaves ; the number of flowers borne on them is also 
much smaller. Thus, on the whole, probably the plants are 
better able to take the risks of temporary fall of water-level, 
and do not have to pay so dearly for exposure, and can better 
stand shallow water. They also probably offer less resistance 
to the current, and so can stand swifter water. The exten- 
sion of leaf surface, obtained in Tristicha by the delicate 
moss-like leaves of the ramuli, is here increased by the 
formation of hairs on the surface of the leaves. 
Dorsiventrality is considerable, and shows very markedly 
in the flower, but less so in the vegetative parts than in 
Lawia, and there is hardly any trace of it in the seedling. 
The great development of the secondary shoots is accom- 
panied in this plant by the curious feature common among 
(46) 
