422 Lang . — On the Morphology of Cyathodium. 
with Targionia expressed by the association of the two genera in the 
Targionioideae. C. foetidissimum stands as an intermediate link between 
Targionia and the smaller species of Cyathodium , being less reduced than 
the latter in its vegetative structure, while the position of both the male 
branches and of the groups of archegonia is essentially the same as in 
Targionia. The position of the archegonia on the actual upper surface 
in C. cavernarum suggests a comparison with the Corsinioideae, though the 
facts do not point to this being an indication of direct relationship l . 
It seems clear that Targionia, C. foetidissimum , and C, cavernarum 
form a series from a thallus of the xerophytic Marchantiaceous type bearing 
a large sporogonium with a well-developed bulbous foot, to a type with 
a small and simple thallus bearing a very small sporogonium attached 
by a very rudimentary foot. There is nothing to suggest that this should 
be regarded as an ascending series, indicating a progression from forms like 
C. cavernarum to the type of Targionia . The facts, on the contrary, appear 
to point to the series being one of reduction standing in relation to the 
shady and damp situations in which the species of Cyathodium are found, 
while Targionia occurs in open and even exceptionally exposed situations. 
In specimens of T. dioica , Schiffn., that had grown mixed with a form of 
Cyathodium on a bank in a jungle in Ceylon, the thallus was slightly thinner 
and the purple colour was absent, except from the extreme margin of the 
thallus and the tips of the ventral scales. I have observed much more 
extreme modifications in plants of Fegatella conica growing in extreme 
shade. The plants were reduced in size, there was great reduction of the 
basal tissue, the assimilating filaments were shorter, and the cells of the 
epidermis (which as in many Marchantiaceae contain chlorophyll) were 
thin-walled and bulged into the air-chamber much as in Cyathodium. The 
much more profound structural peculiarities exhibited by Cyathodium must 
of course be regarded as the result of adaptation to the changed conditions, 
and not as directly induced by them. 
In reviewing the features presented by Cyathodium the persistence of 
the system of low flat air-chambers may be first noted and contrasted with 
their loss in such a hygrophytic form as Dumortiera. The reduction in 
thickness of the thallus is at the expense of the basal tissue, which (except 
at the midrib in C. foetidissimum) is only a single layer. Assimilating 
filaments are completely absent from the chambers. The persistence of 
the air-chambers and the specialization of the cells of their epidermis for 
assimilation suggest that Cyathodium is to be regarded as primarily a form 
adapted to shade conditions rather than as a hygrophyte. Were the 
function of assimilation once transferred to the most superficial layer, as so 
frequently happens in shade-loving plants, the preservation of the system 
1 The resemblance is increased in those exceptional cases in which the growth continues as 
a vegetative thallus bearing a sporogonium on its upper surface. Stephani, loc. cit., p. 63. 
