OF CEYLON AND TNDIA. 
399 
seen in figures 13, 15, 13. Tlie second thallus is usually in 
the smaller angle between the cotyledons. In one case three 
thalli were observed. The development of the thallus is 
endogenous, but as usual this was a matter of difficulty to 
observe, and in one or two examples it was impossible to 
make definitely sure. The endogeny seems to be only under 
one or two layers of cells. As soon as the thallus emerges the 
line of demarcation becomes very indistinct, the cells at the 
edge of the thallus coming into the same level as those 
of the hypocotyl. 
Leaves soon develop above the cotyledons. The first 
usually appears in the larger angle between them, and the 
second in the smaller, but apparently the re verse is sometimes 
the case. Both cases are seen in the two seedlings of 
figure 14. Subsequent leaves are arranged in an approxi- 
mately distichous way upon the stem, the third leaf being 
approximately over the first. The leaves are subulate, and 
have sheathing bases, and bear hairs upon their upper 
surfaces, like so many in this family. The growth of the 
primary stem is not long continued ; it rarely forms more 
than 6-8 leaves, of about 5-7 mm. in length. This primary 
axis can hardly therefore be of very much use to the plant 
after the thallus has become of appreciable size, and indeed 
the primary axes, so far as could be found, seem to disappear 
after the first two or three months. 
To return to the growth of the thallus. When it first 
emerges from the hypocotyl, it has a narrow apex, but it 
soon widens into an ovate form, as in figure 11, and this form 
of the apex remains essentially unchanged throughout the 
life of the plant. 
Examination of the apex of the thallus shows that the 
extreme tip bears, or rather is composed of, thick-walled 
collenchy matous cells, much as in Hydrobryum olivaceum, 
much larger than the small and thin-walled and densely 
protoplasmic cells immediately behind the tip. The latter 
are meristematic, and the collenchymatous tissue represents 
a root-cap, though it does not seem to be of much practical 
