506 Campbell . — The Development of 
off by a transverse wall. The next divisions were not seen, 
and in the youngest stage, found subsequently, there was 
a large two-sided apical cell present, which looked as if it 
might have been formed by the intersection of the first two 
walls in the terminal cell (Fig. 40). It is very probable that 
there is no absolute uniformity in the divisions, and that 
octant-divisions, such as occur frequently in most of the Mar- 
chantiaceae and Anthoceros as well as in Sphaerocarpus , may 
also be found. In the later stages the basal part of the 
thallus had assumed a cylindrical form, while the end was 
flattened out into a lamina but one cell thick. In Fig. 41 is 
shown one of these with a cell ( x ) which may perhaps be the 
apical cell, although its lateral position might be against this. 
Since, however, in the still older plants studied, the growing- 
point was strongly lateral, this objection is not a valid one. 
A most striking feature of the older plants (Fig. 42) was the 
presence of the leaf-like lobes which were found on either side 
of the growing-point and gave the thallus a most characteristic 
appearance, very different from the corresponding stage of 
Sphaerocarpus or the Marchantiaceae, and resembling more 
the young thallus of Anthoceros fusiformis , or still more the 
prothallium of Equisetum . Just at what point the two-sided 
apical cell of the young thallus is replaced by the form 
characteristic of the older one could not be determined. In 
none of the specimens examined was a rhizoid developed 
from the base of the germ-tube, but the first one grew out from 
one of the basal cells of the thallus itself (Fig. 42). 
Summary and Conclusions. 
There is little doubt that on the whole Geothallus agrees 
more nearly with Sphaerocarpus in its structure than with any 
other known form, and may very properly be placed in the 
same family, which also includes, according to Schiffner 1 , 
the imperfectly known Thallocarpns . Leitgeb 2 unites Riella 
1 The Hepaticae, in Engler and Prantl, Die Natiirlichen Pflanzenfamilien, 91, 92, 
P- 5 °- 
2 Leitgeb, 1 . c., iv. p. 9. 
