98 
F. Cavers. 
a rudimentary doubling of the normally single-layered wall of the 
fruit, hut throughout the Marchantiales the capsule-wall consists of 
a single layer of cells, except for the apical thickened cap frequently 
found in the higher families. Hence the interpretation of these 
sterile cells in Tessellina remains an open question. 
CORSINIACE/E. 
In the two genera belonging here, the archegonia are developed 
in sunken groups on the upper side of the thallus, each group being 
protected by the outgrowth of the thallus-tissue ; the capsule is 
separated from the foot by a short neck-like seta, and its wall 
becomes disorganised to set the spores free. The air-chambers are 
arranged in a single layer, and each chamber opens by a pore 
surrounded by a single ring of cells. 
In Corsinia the cells forming the floor of the chambers generally 
grow out to form short assimilating filaments, but sometimes these 
are wanting. The ventral scales are small and are scattered over 
the whole underside of the thallus, as in Riccia natans ; each scale 
has on its free margin a long threadlike appendage, and at the front 
of the thallus these appendages bend up over the growing-point, in 
the same way as the more highly developed appendages characteristic 
of the ventral scales of the higher orders of Marchantiales. 
The antheridia are collected into a receptacle which has the 
form of a ridge, as in Riccia natans ; sometimes it is forked in front 
owing to branching of the apex, but the growing-point of the thallus 
is not used up in the development of the receptacle, hence several 
receptacles may be formed one after another. Each arche- 
gonial group, containing from six to ten archegonia, accompanied 
by numerous hairs (paraphyses) lies in a depression of the thallus ; 
several groups may be formed in succession, the growing apex not 
being used up. The developing sporogonium is protected by a 
curious involucre, which grows up from the depression and becomes 
lobed, the lobes containing air-chambers (Fig. 8). This outgrowth 
is not fully formed unless fertilisation occurs; if only one arche- 
goniutn develops a fruit, the involucre bends over it and shows 
one-sided growth, becoming palmately lobed, but if several fruits 
are formed, the outgrowth becomes radially symmetrical and peltate, 
its lobes covering the developing fruits. The capsule contains 
numerous sterile cells mixed with the spore mother-cells, but 
neither these cells nor those forming the capsule-wall bear fibrous 
thickenings (Fig. 9). 
