428 BOTANY I-AUT n 



one at each of the marginal constrictions from which their further development 

 into new jilants proceeds. On cross-section (E) they are seen to lie composed of 

 several layers of cells ; some of the cells are lilled with oil globules (7), o), while 

 from other colourless cells rhizoids develop. Cells containing oil are also present 

 in the mature thallus, and are of frequent occurrence in all the Hepaticae. By 

 means of the abundantly developed genuine Murr/mntin is enabled to multiply 

 vegetatively to an enormous extent. 



The sexual organs, antheridia and archegonia, are borne on special erect branches 

 of the thallus. The reproductive branches, which are contracted below into a 

 stalk, expand above into a profusely branched upper portion. In this species, 

 which is dioecious, the antheridia and archegonia develop on dilferent plants. 

 The branches producing the male organs terminate in lobed discs, which bear the 

 antheridia on their upper sides in flask-shaped depressions, each containing an 

 antheridium (Fig. 381 B). The depressions, into each of which a narrow canal 

 leads, are separated from each other by tissue provided with air-chambers. (The 

 structure of the antheridia and sperniatozoids is illustrated by Fig. 375 ami the 

 accompanying description. ) 



The female branches terminate each in a nine-rayed disc (Fig. 382 A). The 

 upper surface of the disc, between the rays, becomes displaced in the processor 

 growth, and, as the archegonia are borne on these portions, they seem to arise from 

 the under side of the disc. The archegonia are disposed in radial rows between the 

 rays, each row being developed in a toothed lamella or sheath (Fig. 382 />', C', li ; 

 for structure of the archegonia see Fig 376 and description . 



The fertilised egg-cell gives rise to a multicellular embryo (Fig. 376 C), and 

 this, by further division and progressive differentiation, develops into a stalked 

 oval SPOROOONIUM. The capsule of the sporogonium is provided with a wall con- 

 sisting of one layer of cells, the walls of which have thickened bands, and ruptures 

 at the apex to let free the spherical spores. The ELATEKS, or elongated, spirally 

 thickened cells formed in the capsules, between the spores, by the prolongation of 

 definite cells, are characteristic of the Marchantias and most of the Liverworts, 

 except the Ricciaceae. The elaters are discharged from the ruptured capsule, together 

 with the spores, and serve for their dispersion in the same way as the capillitium 

 of the Myxomycetes (Fig. 382, E, F, G). The ripe capsule, before the elongation 

 of the stalk, remains enclosed in the archegonium wall D, mv), which, for a time, 

 keeps pace in its growth with that of the capsule. As the stalk elongate-, the 

 archegonium wall or calyptra is broken through and remains behind, as a sheath, 

 at the base of the sporogonium (E, c). The capsule is surrounded also by the 

 pseudo-perianth, an open sac-like envelope which grows, before fertilisation, out of 

 the short stalk of the archegonium (Fig. 376 C, pr ; Fig. 382 D, E, p). 



Marchantia was formerly used in the treatment of diseases of the liver ; this 

 fact explains the origin of the name Liverwort. 



Order 3. Anthoeerotaeeae 



The few forms included in this order have an irregular, disc-shaped thallus, 

 which is firmly anchored to the soil by means of rhizoids. The cells of the thallus 

 contain, in contrast to those of other Hryophyta, a single large chloroplast. The 

 antheridia arise, in groups of two to four, by the division of a cell lyhig below the 

 epidermis ; they remain enclosed in cavities beneath the upper surface of the 

 thallus until maturity. The archegonia are sunk in the upper surface of the 

 thallus ; after fertilisation they become covered over by a many-layered wall 



