MUSCI. 



is differentiated from the endothecium (Fig. 131, D) and thus comes to be composed 

 of several layers of cells. An intercellular space is formed in it, which lies between 

 an outer wall of several layers of cells and some cell-layers, usually two in number, 

 next the archesporium (Fig. 142, the longitudinal section); the latter constitute the 

 outer spore-sac, the inner spore-sac being the outermost layer of cells in the 

 columella abutting upon the archesporium (Fig. 144,^). The form of the arche- 

 sporium in the Bryineae and Phascaceae is that of a cask open at both ends, and 

 the columella therefore passes through it; it is otherwise in Andreaea, where the 

 archesporium is a curved layer of cells concave downwards, and the columella does 

 not pass through it; the same is the case in Sphagnum (Fig. 139). Archidium, one 

 of the Phascaceae, shows no differentiation of an archesporium ; a few cells of the 

 endothecium, of which neither the number (1-7) nor the position are fixed, become 

 mother-cells of the spores, in each of which four spores are formed by tetrahedral 

 division. This is obviously the lowest form among the Mosses, and its development 

 agrees with the development of the embryo in the Hepaticae ; there is here no true 

 separation of the cells of the endothecium into sterile and fertile cells, since under 

 certain circumstances every cell of the endothecium may become a spore-mother-cell. 

 Finally, in Sphagnum the archesporium has the same form as in Andreaea, but it is 

 formed out of the amphithecium. It still seems doubtful whether the origin from 

 amphithecium or endothecium is an important difference or not ; it may however be 

 added to the many other characteristics which separate the Sphagnaceae from their 

 allies. We subjoin a table of the various types of development in the sporogonium 

 of the Mosses according to Leitgeb's views *. 



A. The archesporium is formed from the amphithecium : 



1. Type of Sphagnaceae. The endothecium forms the columella only, which 

 does not pass through the archesporium, but is covered by it above. 



B. The archesporium is formed from the endothecium ; all the sporogonia have 

 a two-sided apical cell : 



2. Type of Archidium. Fertile and sterile cells mingled together in the endo- 

 thecium. The spore-sac is separated from the wall of the capsule by a bell-shaped 

 intercellular space. There is no columella 2 . 



3. Type of the Andreaeaceae. The endothecium is differentiated into arche- 

 sporium and columella ; the columella does not pass through the archesporium. The 

 innermost layer in the amphithecium becomes the spore-sac, which however is not 

 separated from the rest of the parietal tissue by an intercellular space. 



4. Type of the Bryineae. Differentiation as in type 3, but the columella passes 

 through the spore-sac, which is separated from the wall of the capsule by an inter- 

 cellular space in the form of a hollow cylinder. 



Such are the changes which take place in the part of the sporogonium which 



1 Das Sporogon von Archidium (Sitz. d. Wiener Akad. LXXX, Bd. I. Abthl. Novemberheft 

 1879, p. ii of the reprint). 



2 In Ephemerum also, one of the Phascaceae, the half-ripe spores lie perfectly free inside the 

 capsule ; but the mode of proceeding is different ; the columella is formed in exactly the same way as 

 in the Bryineae, but is subsequently displaced by the spore-mother-cells, as they increase in size, and 

 disappears. See N. J. C. Miiller, Die Entwicklungsgesch. d. Kapsel von Ephemerum (Pringsheim's 

 Jahrb. f. wiss, Bot. VI. p. 237). 



N 2 



