MUSCI. 



J77 



here than in the Hepaticae (Fig. 129 B, 130 B\ The upper cell then shows the 

 same divisions as in the Hepaticae ; the wall of the venter and the central cell are 

 formed in the same way as in them (p. 150); but there is a striking difference in the 

 further development of the neck. In the Hepaticae the first transverse division of the 

 inner cell produces an upper cell which represents at once the lid of the archegonium ; 

 but in the Mosses this cell developes as an apical cell and by successive longitudinal 

 divisions produces tiers of cells, each of which consists of three outer cells enclosing 

 one inner canal-cell, but otherwise behaves in exactly the same way as the single tier of 

 neck-cells in the Hepaticae. A long neck, consisting of six exterior rows of cells and 

 their canal-cells, is thus produced and subsequently becomes twisted, passing below 

 into the wall of the venter formed of two layers of cells, or in Sphagnum of four. 

 The central cell, earlier formed here than in the Hepaticae, divides by a transverse 

 wall into an upper cell, the ventral canal-cell, and a lower cell, the protoplasm of 

 which contracts and forms the oosphere (Fig. 130, ). The conversion of the whole 

 of the canal-cells into mucilage and the opening of the neck follow in the same way 

 as in the Hepaticae. 



The sporogonium (sporophore, sporophyte}, the product of fertilisation in the 

 oosphere, attains its full development in Sphagnum almost entirely within the venter 

 of the archegonium, which grows vigorously as the oospore developes, and is trans- 

 formed into the calyptra ; in the rest of the Mosses the calyptra is torn away at its 

 base from the vaginula by the elongation of the sporogonium usually some time 

 before the development of the capsule, and, except in the case of Archidium and its 

 allies, is carried up as a cap on the sporogonium; its apex continues for a long time 

 to be surmounted by the neck of the archegonium, the walls of which become a deep 

 reddish brown. The sporogonium in all the Mosses consists of a stalk (seta) and the 

 receptacle of the spores (capsule , theca or urn] ; in Sphagnum, Andreaea and Archidium 

 the seta is very short, in almost all others long or very long, and it always has its 

 base sunk in the tissue of the stem, which by luxuriant growth after fertilisation forms 

 a sheath-like wall, the vaginula, beneath and beside the archegonium. Archegonia 

 with unfertilised oospheres are often to be seen on its exterior slope, for one only of 

 a group usually, or only the first that has its oosphere fertilised, perfects an embryo. 

 The capsule in all Mosses has its wall composed of several layers of cells with a 

 distinct epidermis, on which stomata are sometimes developed. The whole of the 

 inner tissue is never employed in the production of spores, though it is eventually 

 displaced by the spores in Archidium} a large part of the central tissue constitutes the 

 so-called columella, and round it the mother-cells of the spores are formed. But the 

 inner structure of the mature capsule, and especially the arrangements for the dispersion 

 of the spores, are so different in the chief divisions of the Mosses, that it is better to 

 study them under the separate divisions, where they will supply characteristic marks 

 for distinguishing the natural groups. The orientation also and further development 

 of the capsule is not the same in the different groups, and the differences are con- 

 nected on one hand with the growth of the embryo, on the other with the mode of 

 formation and with the form and origin of the archesporium (vid. infra). 



As regards the succession of cell-divisions in the embryo, Sphagnum l differs from 



1 Besides Schimper's account, see Waldner in Bot. Zeit. 1876, p. 595. 



H 



