OF CEYLON AND INDIA. 
291 
in which, are two xylem groups towards the upper side. The 
delicate moss-like leafy shoots are borne endogenously on 
the flanks of the thallus, and have thin simple leaves, one 
cell thick, arranged in three ranks, one upper and tw'o at the 
sides. They are occasionally branched, chiefly at the base. 
The flowers are borne on lateral branches of these shoots, 
subtended by a couple of larger leaves at the base of the stalk 
of the flower. Warming (42, V.) gives a fuller and better 
account of the morphology. He regards the thallus as root, 
chiefly from analogy with similar organs in other Podoste- 
maceæ. The secondary shoots may be divided into two 
classes, those of limited, and those of unlimited, growth. The 
former are assimilatory, not erect, dorsiventral in structure, 
with tristichous leaves, and grow only to a comparatively 
short length ; the leaves towards the outer end are usually 
longer, and the last leaf seems to be terminal or nearly so, 
and is on the upper side. The shoots of unlimited growth 
are longer, more or less erect, with a more complex phyllo 
taxy. Their branching is peculiar ; the branches are of 
two kinds, and are usually arranged in pairs, one above the 
other, alternately on the two sides of the main shoot. Of 
the pair of branches at each node, the lower is a shoot of 
limited growth, the upper is one of unlimited growth, 
repeating the structure of the main shoot. These short 
shoots in the case of T. ramosissima have been termed ramuli 
in systematic descriptions, and the name is convenient for 
use. The flowers are borne on the shoots of unlimited 
growth. 
In a later paper (42, YI.) Warming describes the various 
existing herbarium specimens of Tristicha, and figures many 
of them to show their branching and other morphological 
features. He reduces them all to two species, T. hypnoides, 
Spr., in America and Africa and T. alternifolia, Tub, in 
Africa. The latter comm only has its ramuli forked into two. 
The very curious shoot morphology here described is 
found again in Weddellina, the only species of which, W. 
squamulosa Tub, has been investigated by Goebel (13, p. 349) 
(40) 
