SKCT. r 



CRYPTOGAMS 



433 



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

 rays, each row being surrounded by a tootlied lamella or sheath (Fig. 872, B, C, h ; 

 for structure of the archegonia see Fig. 368 and description). 



The fertilised egg-cell gives rise to a multicellular embryo (Fig. 368, C), and 

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

 oval .sPdiioGONiUM, The capsule of the sporogoniuni is provided with a wall con- 

 sisting of one layer of cells except at the apex, where it is two-layered ; the cell- walls 

 have thickened bands. The capsule ruptures at the apex to let free the spherical 

 spores. The elaters, or elongated, spirally thickened cells formed in the capsules, 

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

 Marchantiaceae and most of the Liverworts, except the Ricciaceae. The elaters are 

 discharged from the ruptured capsule, together with the spores, and assist in their 

 dispersion in the same way as the capillitium of the Myxomycetes (Fig. 372, E, F, 

 G). The ripe capsule, 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 surrounded also by the pseudo-perianth, an open sac-like 

 envelope which grows, before fertilisation, out of the short stalk of the arche- 

 gonium (Fig. 368, C, 2}r ; Fig. 372, D, E, p). 



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

 fact explains the origin of the name Liverwort. 



Order 3. Anthoeerotaceae ("•^) 



The few forms included in this peculiar and isolated 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 Bryophyta, a single 

 large chloroplast. The antheridia arise singly or in 

 groups of two to four, by the division of a cell lying 

 below the eiiidermis ; they I'emain enclosed in cavities 

 beneath the upper surface of the thallus until maturity. 

 The origin of the antheridia thus differs from what is 

 the case in all other Archegoniatae in being endogen- 

 ous ; a superficial cell divides into an outer segment, 

 forming the roof of the cavity, and an inner one, which 

 becomes the mother-cell of the antheridia. The arche- 

 gonia are sunk in the upper surface of the thallus ; 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 superficial cells of the foot grow out into rhizoid-like papillae. 

 The capsule splits longitudinally into two valves, and has a central hair-like 

 columella formed of a few rows of sterile cells (Fig. 373). The columella does 

 not extend to the apex of the capsule, but is surmounted by a narrow layer of 

 sporogenous cells. Elaters also occur ; they are multicellular, variously shaped, 

 and often forked. The sporogonl-i, unlike those of all other Hepaticae, do not 

 ripen simultaneously throughout their whole length, but from the tips downwards, 

 and continue to elongate by basal growth after emerging from the archegonia. 



2f 



Fi(i. Z^i. — Anthoceros laei'is. 

 sp, Sporogoniuni ; c, colu- 

 mella. (Nat. size.) 



