OF CEYLON AND INDIA. 
343 
from it branches run to the endogenons secondary shoots, 
which are produced in acropetal succession upon the 
thallus, usually alternately, but often sub-oppositely. The 
endogenous shoots have been fully described by Warming. 
In contradistinction to what Ave have seen in Tristicha and 
Podostemon, they are very much reduced ; the axis does not, 
so long as the shoot remains vegetative, come above the thallus 
surface at all, but remains almost evanescent, and the only 
part appearing above the thallus is the leaves, of which 
there is a small fascicle, about 4-8 in number, simple, 
subulate, hairy on the upper surface, and not often more than 
5-10 mm, long. The secondary shoots appear very near to 
the tip, and are usually about 5-10 mm. apart ; they are 
distichously arranged along the tAvo sides of the cylindrical 
thallus, ^.e., on the sides which were lateral as the thallus 
started from the creeping part. 
The thallus branches freely upon or near to the rock, but 
only rarely do the upper parts of the drifting thalli branch; 
when this occurs, the branches are like the drifting part, 
and lie more or less parallel with it. The branching, as a 
rule, is exogenous, except when branches are formed on old 
parts of the thalli, when they are commonly endogenous. 
When a branch is formed, it usually creeps along the rock for 
a short distance, and then gives rise, just like the primary 
thallus of the seedling, to a drifting thallus. Thus ulti- 
mately the plant forms a large number of drifting thalli and 
a confused tangle of creeping thalli upon the rock. The 
branching is less regular in this species than in most of the 
others with which we have to deal ; the branches appear 
more or less anywhere, instead of being in strict acropetal 
succession along the thallus. By the end of September the 
plant has reached its full vegetative growth, and is even 
more striking as seen in shallow water than Podostemon 
subulatus. PL XIX. shows such a plant ; there are many long 
drifting thalli of lengths up to 50 or even 60 cm., waving out 
in the water as the swift current passes by, but firmly held 
by the creeping thalli at the base. The colour is green or red. 
