i8 MOSSES AND FERNS chap. 



thallus; but in most Liverworts the fertilisation of an arche- 

 gonium checks the further formation of archegonia in the same 

 group, and only those that are near maturity at the time reach 

 their full development ; and even if more than one archegonium 

 of a group is fecundated, as a rule but one embryo comes to 

 maturity. 



The Sporophyte 



Unquestionably the lowest type of sporogonium is found 

 in Riccia (Fig. 6). Here the result of the first divisions in 

 the embryo is a globular mass of cells, which a little later shows 

 a single layer of peripheral cells and a central mass of spore 

 mother cells, all of which produce spores in the usual way. 

 The sporogonium remains covered by the venter of the arche- 

 gonium until the spores are ripe, and never projects above the 

 surface of the thallus. The spores only escape after the thallus 

 (or at least that part of it containing the sporogonia) dies and 

 sets them free as it decays. In the genus Sphcerocarpus (Fig. 

 30), which may be taken to represent the next stage of develop- 

 ment, we notice tw^o points in which it differs from Riccia. In 

 the first place there is a basal portion (foot), which is simply an 

 absorbent organ, and takes no part in the production of spores. 

 Secondly, only a part of the archesporium develops perfect 

 spores. A number of the spore mother cells remain undivided, 

 and serve simply to nourish the growing spores. In the 

 majority of the Hepaticge the sporogonium shows, besides the 

 foot and the capsule, an intermediate portion, the stalk or seta, 

 which remains short until the spores are ripe, when, by a rapid 

 elongation of its cells, the capsule is forced through the calyptra 

 and the spores are discharged outside. In these forms, too, 

 some of the cells of the archesporium remain undivided, and 

 very early are distinguished by their elongated shape from the 

 young spore mother cells. These elongated cells later develop 

 upon the inner surface of the cell wall peculiar spiral thickened 

 bands, which are strongly hygroscopic. These peculiar fusi- 

 form cells, the elaters, are found more or less developed in all 

 the Hepaticse except the lowest ones. 



The dehiscence of the sporogonium is different in the 

 different orders. In the Ricciacese and some Marchantiacese 

 the ripe sporogonium opens irregularly; in a few cases (species 

 of Fimbriaria) the top of the capsule comes off as a lid; ir 



