392 BOTANY 



perich^ETIA. Between the sexual organs there are usually present a 

 number of multicellular hairs or paraphyses. The Moss-plants may be 

 monoecious, in which case both kinds of sexual organs are borne 

 on the same plant either in the same or different receptacles ; or 

 dioecious, and then the antheridia and archegonia arise on different 

 plants. 



The sporogonium of the Mosses develops a capsule with an axial 

 COLUMELLA consisting of sterile tissue. The spore-sac surrounds the 

 columella, which accumulates food material and water for the develop- 

 ing spores. Elaters are never formed. Distinctive variations in the 

 mode of development and structure of the capsules are exhibited by 

 the four orders of the Musci : Sphagnaceae, Andreaeaceae, Phascaceae, and 

 Bryinae. 



Order 1. Bryinae 



In this order (termed also Stegocarpae), which includes the majority of all the 

 true Mosses, the Moss fruit attains its most complicated structure. The ripe 

 spokogonium, developed from the fertilised egg, consists of a long stalk, the seta 

 (Fig. 321, B, s), with a foot at its base, sunk in the tissue of the mother plant, 

 and of a capsule (k), which in its young stages is surmounted by a hood or calyp- 

 tka (A, c). The calyptra is thrown off before the spores are ripe. It consists of 

 one or two layers of elongated cells, and originally formed part of the wall of the 

 archegonium which, at first, enclosed the embryo, growing in size as it grew, until, 

 finally ruptured by the elongation of the seta, it was carried up as a cap, covering 

 the capsule. In the Liverworts the calyptra is, on the contrary, always pierced by 

 the elongating sporogonium, and forms a sheath at its base. The upper part of 

 the seta, where it joins the capsule, sometimes becomes distinctly enlarged and is 

 then termed the apophysis. In Milium it is scarcely distinguishable, but in 

 Polytrichum commune it has the form of a swollen ring-like protuberance (Fig. 323, 

 ap), while in species of Splachnum it dilates into a large cushion-like structure 

 of a yellow or red colour, upon which the capsule appears only as a small protuber- 

 ance. The upper part of the capsule becomes converted into a lid or operculum 

 (Fig. 321, d), which is sometimes drawn out into a projecting tip. At the margin 

 of the operculum a narrow zone of epidermal cells termed the ring or annulus 

 becomes specially differentiated. The cells of the annulus contain mucilage, and 

 by their expansion at maturity assist greatly in throwing off the lid. In most 

 stegocarpous Mosses the mouth of the dehisced capsule bears a fringe, the peri- 

 stome, consisting usually of tooth-like appendages. 



The peristome of Mnium hornum (Fig. 321, 0, p) is double ; the outer peristome 

 is formed of 16 pointed, transversely striped teeth (Z>) inserted on the inner 

 margin of the wall of the capsule. They are strongly hygroscopic ; opening in 

 dry weather, they allow of the dispersion of the spores, while in wet weather they 

 close again and shut in the spore masses. The inner peristome lies just within the 

 outer, and consists of cilia-like appendages, which are ribbed on the inner side and 

 thus appear transversely striped ; they coalesce at their base into a continuous 

 membrane (E). Two cilia of the inner peristome are always situated between each 

 two teeth of the outer row. The cilia facilitate the dissemination of the spores 

 by their hygroscopic movements. 



The teeth and cilia of the peristome are formed in this instance of thickened 



