412 Lang \ — On the Morphology of Cyathodhim . 
as to limit and control the loss of water vapour. This general view of the 
significance of the structural peculiarities of the Marchantiaceae is confirmed 
by the situations in which they are found most abundantly. My own 
experience, when collecting Hepaticae in Ceylon and the Malay Peninsula, 
was that the Marchantiaceae were most abundant in open exposed situa- 
tions, and almost confined to such places ; that some forms also occurred 
by path-sides in the forest, but that they were almost absent from the depths 
of the forest itself, where thalloid J ungermanniaceae were abundant. 
Among the Marchantiaceae there are, however, one or two genera 
which not only occur in relatively damp and shaded situations, but exhibit 
corresponding modifications in the structure of the thallus. In Dumortiera 
(and perhaps in the light of recent investigations Monoclea may be added) 
the air-chambers are rudimentary or absent, and transpiration and assimila- 
tion are carried on by the unprotected superficial cells of the thallus, which 
„ is thus physiologically comparable to that of Amur a or Pellia. In 
Cyathodhim modifications of a different nature to those in Dumortiera 
appear to stand in relation to a damp and shady habitat. The few species 
occur in the deep shade of tropical forests, in dark caves, and sometimes in 
the crevices of walls or on paths in rather more exposed positions. In this 
genus the layer of air-chambers opening by definite pores is retained, but 
the basal portion of the thallus is for the most part only a single layer of 
cells thick. Filaments of assimilating cells are absent from the air-chambers, 
the epidermis of which has taken over the function of assimilation. 
In the present state of our knowledge of the genus it seemed worth 
while to give the results of my investigation of two forms of Cyathodium^ 
which bore sexual organs and sporogonia of various ages, in some detail, 
although this involves some repetition of known facts. The two forms 
investigated were collected in the Malay Peninsula and the material was 
preserved in alcohol. The larger form was found growing on rocks in the 
deep shade of the forest on Maxwell’s Hill in Perak. It grew especially 
on the vertical faces of damp rocks, and had a distinctly phosphorescent 
appearance. Comparison with original specimens of C. foetidissimum , 
Schiffn., showed that while differing in some small details, it was referable 
to this species. 
The other form was found growing in extensive patches on the walls 
and floor of a dimly lit limestone cave near Kuala Lumpur. The small 
thalli closely overlapped one another, and they also had the same phos- 
phorescent appearance. In a preliminary statement 1 I referred this to 
C. aureo-nitens , (Griff.) Schiffn. Since then, examination of Griffith’s 
original specimens at Kew has shown me that it cannot be referred to that 
species, but is practically identical with specimens of C. cavernarum , Kunze, 
from Cuba. I do not propose to enter here into the question of the 
1 British Association Report. Cambridge, 1904, p. 782. 
