424 Lang . — On the Morphology of Cyathodium . 
be referred to in conclusion. When we look for sporogonia resembling 
that of Cyathodium probably the closest comparison as regards the relation 
between capsule and foot is presented by Sphaerocarpus and Riella. The 
mode of segmentation of the embryo in these genera has much in common 
with the Marchantiaceae, the comparison between Sphaerocarpus and 
C. cavernarum being particularly close. In both Riella and Sphaerocarpus 
the mature sporogonium consists of a small capsule connected by a narrow 
stalk with a small bulbous foot. In some species of Riella the stalk con- 
sists of a single row of cells, as in C. cavernarum , and the bulbous foot, 
which in Riella is composed of more numerous cells, shows a tendency to 
form absorbent processes. In all the Marchantiaceae and the Jungerman- 
niaceae, with these exceptions, the foot and seta of the mature capsule 
appear to be relatively bulky. On the other hand, in the Ricciaceae the 
sporogonium shows no trace of a foot. 
As has been shown above, there are reasons for regarding the sporo- 
gonium of Cyathodium as a reduced structure, and the same may perhaps 
be assumed for Riella. But in the absence of any other forms with a very 
small sterile portion of the sporogonium these genera are not without 
interest as indicating the sort of structure which may have characterized 
the stage intermediate between the Ricciaceous type and sporogonia with 
a well-developed foot. It is at least possible that the reduction in 
Cyathodium has taken place along the lines of differentiation, and that it 
may in this respect represent to some extent an intermediate stage between 
the Ricciaceae and Marchantiaceae. 
Such reduced forms must, however, be used with caution in speculations 
as to the methods of descent, and further information as to the range of 
variation in the sporogonium under altered conditions must be accumulated 
before any but tentative conclusions can be drawn from their study. With- 
out attempting further to follow out this line of comparison, the present 
paper may be left as a description of the main facts regarding the structure 
of Cyathodium , the full explanation of which must depend on further 
observations and experiments. 
1 
