GROUP II. BRYOPHYTA : HEPATKLE. 323 



Ge.nmce are produced in Lunularia and Marchantia in special receptacles, 

 termed cupules, borne on the dorsal surf ac3 of the shoot ; in Lunularia the 

 cupule is crescsnt-shaped, in Marchantia it is circular (Fig. 198J5). The 

 cupule is formed by an outgrowth of the air-chamber layer, and in 

 Marchantia its margin is prolonged into laciniae. The gemmae spring 

 from single cells of the floor of the cupule, which elongate upwards and 

 divide transversely into a stalk call and a terminal cell, which, by 

 repeated growth and division, forms a flattened plate of tissue, several 

 layers of cells thick at the middle, thinning out to a single layer at the 

 margin, with a growing-point in a depression on each lateral margin. 

 The symmetry of the gemmae is isobilateral ; but when they fall on to the 

 soil and begin to grow, the undermost surface becomes the ventral, and 

 the uppermost the dorsal. Some of the superficial cells have no chloro- 

 plastids ; those of the surface next the soil grow out into root-hairs. 



B. The SroROPHYTK. The degree of morphological and histological 

 differentiation of the sporophyte presents wide divergences in the different 

 groups. In the Ricciese, the whole embryo simply forms a spherical 

 capsule : in the Marchantiese, the capsule is developed entirely from the 

 epibasal cells, whilst the hypobasal cells give rise to a bulbous foot, which 

 attaches the embryo to the parent, and to a short stalk which bears the 

 capsule, and is formed at a relatively late stage by intercalary growth. 



The differentiation of the tissue of the capsule into amphithecium and 

 endothecium is well-marked, except in the Riccieae. The archesporiuni is 

 coextensive with the endothecium. 



In the Riccia the whole of the archesporial cells are sporogenous ; in 

 Corsinia, some of the archesporial cells are sterile, but these undergo no 

 special differentiation; in the Marchantiese 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 hj'gro- 

 scopic, 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 Riccieae, and becomes entirely dis- 

 organised during the development of the spores. In the Marchantiese the 

 cells of the walls are generally thickened and the thickenings fibrous, in 

 which case the capsule opens by the splitting of the wall longitudinally 

 into a number of teeth. 



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

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

 the exospore 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 exospore is feebly developed, and presents 

 a granular thickening. In consequence of the thinness of the exospore, 

 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 



