388 BOTANY 



are filled with oil globules {D, o), while from other colourless cells rhizoids develop. 

 Cells containing oil are also present in the mature thallus, and are of frequent occur- 

 rence in all the Sepaticae. By means of the abundantly developed gemmae Mar- 

 chantia 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 rolled together at the lower 

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

 species, which is dioecious, the antheridia and archegonia develop on different 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. 316, £). The depressions, into each of which a narrow canal 

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

 ture of the antheridia and spermatozoids is illustrated by Fig. 310 and the accom- 

 panying description, p. 381.) 



The female branches terminate each in a nine-rayed disc (Fig. 317, A). The 

 upper side of the disc, between the rays, is turned underneath in the process 

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

 from the under side. The archegonia are disposed in radial rows between the rays, 

 each row being enveloped in a toothed lamella or sheath (Fig. 317, B, 0, h ; for 

 structure of the archegonia, see Fig. 311, and description, p. 382). 



The fertilised egg-cell gives rise to a multicellular embryo (Fig. 311, C), and this, 

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

 spokogonium. The capsule of the sporogonium is provided with a wall consisting 

 of one layer of cells, and ruptures at the apex to let free the spherical spores. 

 The elatees, or elongated, spirally thickened, fibre-cells formed in the capsules, 

 between the spores, by the prolongation of definite cells, are characteristic of the 

 Marchantias and most of the Liverworts. 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. 317, E, F, G). The ripe cap- 

 sule, before the elongation of the stalk, remains enclosed in the archegonium wall 

 {D, aw), which, for a time, keeps pace in its growth with that of the capsule. As 

 the stalk elongates, 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 sur- 

 rounded also by the pseudo-perianth, an open sac-like envelope which grows, before 

 fertilisation, out of the short stalk of the archegonium (Fig. 311, C, pr ; Fig. 317, D, 

 E, p). Similar envelopes occur in the higher Sepaticae, in which they constitute a 

 true perianth, and are formed of leaves. 



■ 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 antheridia arise, in groups 

 of two to four, by the division of a cell lying below the epidermis ; they remain en- 

 closed in cavities in the upper side of the thallus until maturity. The archegonia are 

 at first merely sunk in the upper surface of the thallus, but after fertilisation they 

 become covered over by a many-layered wall formed by the overarching growth of 

 the adjoining tissue. This enveloping wall is afterwards ruptured by the elongating 

 capsule, and forms a sheath at its base. The sporogonium consists of a swollen foot 

 and a long, pod-shaped capsule ; it has no stalk. The capsule splits longitudinally 

 into two valves, and has a central hair-like columella formed of a few rows of sterile 

 cells (Fig. 318). The columella does not extend to the apex of the capsule, hut is 



