V. MOSSES (MUSCI): SPHAGNALES—ANDREJEALES 165 



development in the typical forms, and shows great uniformity, 

 both in its development and in the essential structure of the 

 full-grown sporophyte. With the exception of Sphagnum, 

 which will be referred to more specially later, the early growth 

 of the sporogonium is due to the segmentation of a two-sided 

 apical cell. The separation of the archesporium takes place at 

 a late period, and like that of Anthoceros 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 he found. 



In all but the lower types, 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 SpJiagnnm 

 and Andrecca, where no seta is present, the axis of the gameto- 

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

 which carries up the capsule above the leaves. 



The formation 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 separa- 

 tion of the cells of two layers of the wall, by which an inter- 

 cellular space is formed which later may become very large 

 (Figs. 109-112). A second similar space may be developed in- 

 side the archesporium, but this is found only in the Polytrich- 

 acege. In the Sphagnaceae and the Andreseaceae this space is 

 not developed. These lacunae are traversed by protonema-like 

 filaments of chlorophyll-bearing cells, and the cells of the mass- 

 ive wall of the capsule also contain much chlorophyll, so that 

 there is no question that the sporogonium is capable of assimila- 

 tion. Stomata, much like those of Anthoceros 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 Bryales 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" and ''peristome," 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 



