GROUP II. BRYOPHYTA : HEPATIC^. 341 



The differentiation of the tissue of the capsule into araphithecium and 

 endothecium is well-marked, except in the Biccieas. The arehesporium is 

 coextensive with the endothecium. 



In the Biccieae the whole of the archesporial cells are sporogenous (except 

 perhaps Oxymitra) ; in Corsinia, some of the archesporial cells are sterile, but 

 these undergo no special differentiation ; in Boschia and in the Marchantieee 

 the sterile cells assume an elongated form, and their walls undergo spiral or 

 annular thickening : these specially modified sterile cells are the elaters, and, 

 being very hygroscopic, they assist in the scattering of the spores. Each 

 sporogenous cell gives rise to four spores. 



The wall of the capsule, which consists generally of a single layer of cells, is 

 but slightly developed in the Kiccieae, and becomes entirely disorganised during 

 the development of the spores. In Corsinia the wall is not highly developed, 

 but it persists till the spores are ripe, when it ruptures irregularly ; in Boschia 

 it is more highly developed, the cells presenting half-ring thickenings on their 

 lateral and internal walls. In the Marchantieae the cells of the walls are 

 generally thickened ; the thickenings may be fibrous, in which case the capsule 

 opens by the splitting of the wall longitudinally into a number of teeth, though 

 in Targionia the splitting is irregular; or the thickenings (sometimes absent) 

 are confined to the walls at right angles to the surface, in which case the 

 capsule opens by the separation of its upper third as a lid or operculum, as in 

 the Operculatas. 



The spores are generally tetrahedral, with two coats, the outer of which 

 (exosporium) is tuberculate or reticulate on the surface. On germination the 

 exosporium of the tetrahedral spore ruptures at the point of junction of the 

 three projecting angles. The spores of Lunularia and Marchantia are small and 

 spherical; the exosporium is feebly developed, and presents a granular thicken- 

 ing. In consequence of the thinness of the exosporium, the whole spore is 

 enabled to enlarge considerably on germination, and it does not rupture at any 

 special point. In Fegatella, cell-divisions take place in the spores before they 

 are scattered. 



The venter of the archegonium keeps pace with the growth of the developing 

 embryo, forming the calyptra, and encloses it until the spores are ripe. In the 

 Biccie the spores are set free by the gradual disorganisation of the calyptra 

 and of the tissue of the thallus in which the calyptra is imbedded ; in the other 

 Marchantiaceae the capsule is forced out of the calyptra by the elongation of 

 the short stalk. 



The Marchantiacese are classified as follows : 



Fam. 1. Ricciea. The gametophyte is characterised by the simple structure 

 of the adult shoot; the air-chamber has a simple pore in only a few forms 

 [Riccia (Ricciella) canaliculata, Bicciocarpus, Oxymitra] ; the assimilatory tissue 

 is confined to the walls of the air-chamber. The sexual organs are not borne on 

 a receptacle, but are developed in a row, or in groups, in the dorsal furrow, and 

 become overgrown by the tissue of the thallus. The sporophyte is character- 

 ised by the absence of differentiation of a foot or seta, consisting, as it does, 

 simply of a capsule ; all the archesporial cells give rise to spores (except the few 

 sterile cells in Oxymitra), and the wall of the capsule becomes disorganised 

 during the ripening of the spores. 



