HEPATIC JE. 
355 
wise and form two rows; between them arise a number of root-hairs with conical thick- 
enings projecting inwards. 
The archegonia and antheridia are formed on the upper side from young epidermal 
cells which grow into papillae, and are overarched, in consequence of their mode of 
development, by the surrounding tissue (Fig. 239). This involucre sometimes forms 
an elevated neck above the sessile antheridia. The archegonia project, at the time of 
fertilisation, above the epidermis ; subsequently they are arched over, and develope from 
their fertilised oosphere the globular sporogonium with a wall consisting of a single layer 
of cells, and entirely filled with spores, without elaters. The spores are set free by the 
decay of the surrounding tissue. 
4. The Marehantiese have all a thalloid stem extended flat upon the ground ; 
it is ribbon-like, dichotomously branched, possesses a mid-rib, and is always composed of 
several layers; the under side produces a number of hairs with conical thickenings 
projecting inwards placed upon a spiral constriction of the internal cavity (Fig. 240, bis, 
C), and also two rows of leaf-like lamellae, like the Riccieae. The upper side is covered 
by a very distinctly differentiated epidermis, penetrated by large stomata ^ of peculiar 
form. Each of these stands, in Marchantia, Lunularia, &c., in the centre of a rhombic 
plate ; these plates are parts of the epidermis which overarch large air-cavities, from the 
bottom of which the cells containing chlorophyll spring in a conferva-like manner, while 
the rest of the tissue is destitute of chlorophyll and consists of long horizontal cells 
without interstices {cf. Fig. 65). 
^ These stomata are formed (see Fig. 89) by the simple separation from one another of four or 
more epidermal cells which afterwards are divided by walls parallel to the surface of the thallus. 
Fig. 240. — Riccia glauca; A apical region in vertical longitudinal 
section ; ar archegonium ; c oosphere (X 560) ; B the unripe sporogonium 
sg surrounded by the calyptra, which still bears the neck of the arche- 
gonium ar (X 300, after Hofmeister). 
Fig. 240 bis. — Cell-forms of Marchantia 
polymo7-pha with thickenings ; A an elater 
(one-half) from the sporogonium, with two spiral 
bands; A' ^ portion more strongly magnified ; 
B a parenchyma-cell from the centre of the thal- 
lus, with thickenings projecting inwards in a 
reticulate manner; C a slender root-hair with 
thickenings projecting inwards, these are ar- 
ranged on a spiral constriction of the cell-wall ; at 
D a thicker-root-hair, with thicker branched pro- 
jections, and spiral arrangenient still more evi- 
dent. 
(Leitgeb.) 
A a 2 
