Geothallus tuber osus, Campbell. 507 
with Sphaerocarpus into the family Rielleae, but Schiffner 1 
makes a special family, Rielloideae, to include the genus 
Riella. The four genera all agree in the absence of perfect 
elaters, which are replaced by the thin-walled chlorophyll- 
bearing cells, and constitute the lowest group of the anacrogy- 
nous Jungermanniaceae, the Anelatereae. 
Geothallus agrees with Sphaerocarpus in the form of the 
apical cell, the general position and structure of the sexual 
organs, including the characteristic envelope with which each 
is surrounded. In all these particulars both genera resemble 
Riccia , where the transverse primary divisions in the antheri- 
dium, as well as the subsequent quadrant-divisions in the 
upper cells, are quite different from the corresponding divisions 
in the antheridium of the typical Jungermanniaceae. The six 
outer rows of cells in the neck of the archegonium in both 
genera are also suggestive of the Marchantiaceae rather than 
of the typical J ungermanniaceae, where there are but five. But 
the most important point of resemblance between Geothallus 
and Sphaerocarpus is the sporogonium, in both the structure 
and development of which they agree very closely. 
The most important points in which Geothallus differs from 
Sphaerocarpus are — its much more massive thallus ; the second 
division in the antheridium and the massive stalk of this 
organ ; the sessile archegonium, and consequent deeper 
penetration of the foot of the embryo into the thallus ; the 
large size and complete separation of the smooth spores ; and, 
most important, the development of true leaves and the 
formation of tubers by which the plant becomes perennial. 
It will be remembered, however, that under certain conditions 
Sphaerocarpus may also develop leaf-like organs. 
The points of resemblance with Riccia have already been 
mentioned. Among the typical anacrogynous Jungerman- 
niaceae, Fossombronia , at least of the American genera, 
resembles Geothallus most closely. It differs, however, in 
several important particulars, apart from the very much more 
1 Schiffner, l.c., p. 51. 
Mm2 
