MOSSES AND LIVERWORTS (BRYOPHYTES) 265 



a spore. It must also be kept in mind that alternation of 

 generations refers to alternation between the sexual genera- 

 tion and the asexual one. In case of several kinds of asexual 

 spore reproduction, such as were seen in some of the parasitic 

 fungi, the term alternation of generations does not apply in 

 its usual meaning, though obviously in such cases there is a 

 series of stages that make up the life round. A more detailed 

 discussion than we have given might show a real alternation 

 of generations in algse and fungi, but for an elementary study 

 this is not advisable." 



247. Kinds of mosses. There are hundreds of different 

 species of mosses, and nearly all of them follow closely the 

 life cycle already outlined. The moss used for the illustra- 

 tions (Figs. 215-220) is Funaria hygrometrica. Another com- 

 mon moss and one of the larger ones is pigeon-wheat moss 

 (Polytrichurni). In forests it commonly produces thick cush- 

 iony patches, and when sporophytes are present they are quite 

 prominent and bear unusually large calyptras. 



Peat-bog moss (Sphagnum) is a very striking form, which 

 with other plants may form peat. It is common in bogs every- 

 where, and grows about the edge of the water or upon the 

 extremely wet soil that has been formed by the partial decay 

 of plants. Due to the peculiar structure of the leaves these 

 plants hold water in great quantities, and from a handful of 

 the plants water may be pressed as from a wet sponge. The 

 gametophyte or leafy shoot of Sphagnum continues its growth 

 at the plant tip from year to year, and the older buried or 

 submerged portions gradually become partially decayed and 

 'intermingled with other plant material. Dense peat masses 

 are thus formed. Such material forms peat fuel, which is com- 

 pressed, dried, and kept for sale in some markets. The sporo- 

 phyte of Sphagnum is quite unlike that of the moss described 

 above, since it is merely a spherical capsule upheld by the elon- 

 gated stem of the gametophyte (Fig. 221). Sphagnum is used 

 quite commonly as a packing material; it is also used as a 

 covering for holding moisture within the soil of potted plants. 



