HE PA TICM. 



zss 



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 Marehantie83 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 



Fig. lifi.—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 (X300, after Hofmeister). 



FIG. 240 bis. —Cell-forms of Marcha7ttia 

 polymorpha with thickenings; A an elater 

 (one-half) from the sporogonium, with two spiral 

 bands ; A' 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 arrangement still more evi- 

 dent. 



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 



I 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 



^ These stomata are formed (see Fig. 89) by the simple separation from one another of four or 

 )re epidermal cells which afterwards are divided by walls parallel to the surface of the thallus. 

 iitgeb.) 



A a 2 



