296 AVTLLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
development of haptera, as indeed we might expect on 
mechanical grounds, and as the secondary shoot grows larger 
the haptera tend to increase also both in size and number, to 
provide the necessary power of adhesion to the rock. In 
the S. Kanara material the hapteron ultimately forms a disc 
in most cases, whilst in the material from the Anamalais 
and Travancore it is usually branched, and this the more 
as it increases in size. In some of the Travancore specimens 
the hapterous feet at the bases of the full-grown secondary 
shoots were as much as 2-3 cm. across (PI. VII., fig. 10), 
forming a holdfast of great power. Part of this foot appears 
to have been due to further development of haptera from 
the base of the stem, a very common occurrence. The 
endogenous shoot arises from the upper side, and is at first 
more or less horizontal (PI. VII., figs. 5, 6, 7), but soon 
bends upwards. It is always more or less flexible, and 
sways with the movement of the water. 
The thallus itself is of simple structure, with a simple 
central vascular bundle, which seems very like that of 
T. hypnoides as described by Cario, or that of Weddellina, 
as described by Wächter (41^ ; I have not made a detailed 
study of it. The cells near the edge contain much silica, so 
that the thallus is very hard to cut in section, and also very 
brittle. This development of silica is very characteristic 
and abundant in very many of the Podostemaceæ, and has 
been described by Cario (8), Kohl (25), Warming, and others 
(and cf. Lawia, below). It is so plentiful in many thalli that 
a razor is almost completely blunted in cutting a single 
section. A physiological function in helping to make the 
organs containing it more or less amphibious has been denied 
to this silica development, but not, I think, altogether on 
good evidence. That the thalli are more or less amphibious, 
i.e., that unlike most water plants they are able to survive a 
considerable period of exposure (and that, too, on naked 
rocks), we shall have occasion to see below in the case of 
several of the Ceylon species, and I am inclined to think 
that the silica in the outer cells may have some function in 
