i8o 
F. Cavers. 
from the thallus tissue which surrounds them and from which they 
are separated only by the delicate single-layered capsule-wall and 
double-layered calyptra. In Tesselliua the capsule-wall is separated 
by several layers of tissue (the two inner layers belonging to the 
calyptra) from the chambered assimilating tissue of the involucre, 
but the food supply for the developing spores comes mainly from 
below, and with this fact we may correlate the presence of a few 
sterile cells among the fertile spore-mother-cells. In Corsinia the 
sporogenous tissue is well raised above the thallus level by the 
differentiation of a foot, which acts as an absorbing organ, and the 
nutrition of the spore-mother-cells is further secured by the 
numerous starch-laden sterile cells mingled with the spore-mother- 
cells and exceeding them in number. The protection of the 
Fimbriaria 
I 
Massalongoa 
Bucegia 
Gnmaldia CryptOmitrium 
I I 
Reboulia NeeBiella 
\ / 
Plagiochasma 
Pelbolepis 
t 
Sauteria 
| Gollaniella 
Clevea 
Corsinia 
\ / 
Tessellina 
I 
Riccia 
Marcnantia 
Preissia 
I / 
Wiesnerella 
Fegatella 
Exormotheca 
Lunularia 
Dumortiera 
Jungermanmales 
Geothal Pus 
I 
Sphaerocarpus 
Riella 
"Sphaero—riccia" 
Fig. 29.—Phylogeny of the Marchantiales. 
developing sporogonium against desiccation—a function performed 
in Riccia by the surrounding thallus tissue—is in Tessellina taken 
over by the involucre and in Corsinia by the massive calyptra. 
This great development of the calyptra, in which Corsinia differs 
from all other Marchantiales, is evidently a biological adaptation to 
compensate for the inadequate protection afforded by the incipient 
carpocephalum ; in Doschia the calyptra is not nearly so thick as in 
Corsinia, but the hood-like involucre covers the fruit more completely, 
and persists until dehiscence. 
In seeking to trace the phylogeny of the Marchantiales (which, 
according to the views here advocated, may be roughly represented 
as in the diagram, Pig. 29), we are confronted by difficulties which 
involve the phylogeny of the Bryophyta as a whole, and which will 
