Marcliantiales. 
93 
II.—MARCH ANTI ALES. 
This group, as already defined, is divided by Schiffner, 
Muller, and other systematists, into two orders, Ricciaceae and 
Marchantiaceae. 
In the Ricciaceae, which includes the two genera Riccia and 
Tessellina, the green upper zor.e of the thallus consists either of 
erect filaments separated by narrow air-spaces, or of a network of 
lamellae which are generally roofed over to form wide chambers ; 
in the latter case, however, the chambers are devoid of special 
assimilating outgrowths. The air-pores are surrounded by a single 
ring of cells. Ventral scales are generally present, but are often 
small, and never show differentiation of an appendage. The sexual 
organs are developed singly and each becomes deeply embedded in 
the thallus; the canal of the antheridial cavity is often prolonged 
into a conical or cylindrical ostiole, and the archegonium neck is 
generally exserted from the archegonial cavity. The sporophyte is 
a simple spore-fruit or capsule, without seta or foot; sterilisation 
is limited to the production of a single-layered wall. The capsule 
remains enclosed in the calyptra, and the spores escape by decay 
of the capsule wall, the calyptra, and the surrounding tissue of the 
thallus. 
In the Marchantiaceae, the green zone of the thallus consists 
of well-developed air-chambers (except in Dumortiera and Monoclea), 
which generally either contain loose filamentous assimilating tissue 
or are divided into secondary chambers by chlorophyll-bearing 
lamellae. The air-pores are surrounded by a single ring, or by 
several concentric rings, or by several superposed rings, of modified 
epidermal cells. The sexual organs are nearly always aggregated 
into receptacles, or gametophores; in all except the lowest forms 
the archegoniophores are stalked, as are also the antheridiophores 
in the highest forms. The sporophyte is differentiated into foot, 
seta, and capsule, and the latter is when ripe pushed through the 
calyptra; except in Corsinia the sterile inner cells of the capsule 
are developed as elaters with fibrous thickenings. 
Since the publication of Schiffner’s classification of the 
Marchantiales, considerable additions have been made to our 
knowledge of the group, and on various grounds it seems necessary 
to propose certain modifications in Schiffner’s scheme. Schiffner 
