GROUP II. BRYOPHYTA. 331 



becomes dilated to form a, false foot (epibasal) which performs the 

 functions of attachment and absorption. 



The tissue of the developing capsule becomes differentiated into 

 an external layer (or layers) of cells, termed the amphithecium, 

 which, in nearly all cases (except Anthocerotaceee and Sphagnaceee) 

 forms only the wall of the capsule ; and an internal solid mass of 

 cells, the endothecium. The spores are developed from a mass or 

 a layer of cells termed the archesporium. In the Hepaticae the 

 archesporium includes the whole of the endothecium (except in 

 Anthocerotaceee, Fig. 238 C), and the archesporial cells are either all 

 sporogenous (Ricciea?) or, as is more frequently the case, some of 

 them are sterile and generally become spirally thickened and elon- 

 gated in form when they are termed slaters. In the Moss Archi- 

 dium there is no defined archesporium, the sporogenous cells being 

 scattered throughout the endothecium. In the Anthocerotacese 

 and in the Musci (except Archidium) the archesporium is a layer 

 of cells : it is generally the external layer of the endothecium, but 

 in most of the Anthocerotaceoe and in the Sphagnaceoe it is the 

 innermost layer of the amphithecium. In these forms where the 

 archespoi'ium is a layer of cells, the internal sterile tissue of the 

 endothecium constitutes what is termed the columella. The arche- 

 sporial cells are either themselves the mother-cells of the spores, 

 or they undergo division to form these cells. Each mother-cell 

 gives rise to four spores ; the nucleus divides into two, and each 

 of these divides again ; the protoplasm aggregates round the four 

 nuclei, constituting four cells which surround themselves with a 

 proper wall and which are the spores. They do not usually all 

 lie in one plane, but are placed tetrahedrally. The mature spore 

 is a cell, consisting of a mass of protoplasm, with a nucleus, and 

 containing chloroplastids, starch-grains and oil- drops; the wall 

 consists of two layers of the usual structure (see p. 69). During 

 the formation of the spores the mother-cells become isolated from 

 each other, floating freely in a mucilaginous liquid in the interior 

 of the capsule. 



The escape of the spores from the capsule is effected in various 

 ways. In some cases the wall of the capsule simply decays (e.g. 

 Ricciese, Phascum), or it splits into valves (eg. Jungermanniacese), 

 or the upper part is thrown off as a lid or operculum (e.g. some 

 Marchantiea3, Sphagnacese, most Bryineaa). 



On being set free, the spores germinate, when the conditions 

 are favourable, giving rise to the protonema. The brittle exo- 



