VI MOSSES {MUSCI): SPHAGNACEyE—ANDRE/EACE^ 157 



period, and like that of AntJioceros it occupies but a very small 

 part of the sporogonium, which in all the higher forms attains 

 a considerable size and complexity. All the archesporial cells 

 form spores, and no trace of elaters can be found. 



In all but the lower forms, the sporogonium becomes 

 differentiated into a stalk (seta) and a capsule. This differ- 

 entiation is gradual, and the elongation of the seta is not a 

 rapid process, due simply to an elongation of the cells, but is 

 caused by actual growth and cell division. In Sphagnum and 

 AndrecBa^ where no seta is present, the axis of the gamctophore 

 elongates and forms a sort of stalk (pseudopodium), which 

 carries up the capsule above the leaves. 



The separation of the capsule and seta takes place by a 

 rapid enlargement of the upper part of the very much elongated 

 embryo about the same time that the archesporium becomes 

 recognisable. This enlargement is accompanied by a separation 

 of the cells of two layers of the wall, by which an intercellular 

 space is formed which later may become very large (Figs. 

 97-100). A second similar space may be formed inside the 

 archesporium, but this is found only in the Polytrichaceaj. In 

 the Sphagnaceae and Andreaeaceae this space is not found. 

 These spaces are traversed by protonema-like filaments of 

 chlorophyll-bearing cells, and the cells of the massive wall of 

 the capsule also contain much chlorophyll, so that there is 

 no question that the sporogonium is capable of assimilation. 

 Stomata, much like those of AntJioceros or the vascular plants, 

 occur upon the basal part of the capsule in many species, but 

 are not always present. 



In Sphagnum and all the higher Bryacese the capsule opens 

 regularly by means of a circular lid or operculum. This in the 

 latter group is a most characteristic structure, and with its 

 accompanying structures, the " annulus " or ring of thickened 

 cells surrounding the opening of the rim, and the " peristome," — 

 the fringe of teeth inside the annulus, — form some of the most 

 important distinguishing marks of different genera and species. 

 When ripe, the operculum falls off and the ripe spores are set 

 free. The teeth of the peristome, by their hygroscopic move- 

 ments, play an important part in scattering the spores, and 

 physiologically take the place of the elaters of the Hepatica^. 



Some Mosses live but a few months, and after ripening 

 their spores, die. This is the case with Funaria Jiygromett'ica, 



