SEC'I'. I 



CKYPTOGAMS 



441 



387, J, ivp) it is scarcely distinguishable, but in Pulytrichum commune it has the 

 form of a swollen ring-like protuberance (Fig. 381, wp), while in species of 

 Spladinum it dilates into a large collar-like structure of a yellow or red colour. 

 The ujjper part of the capsule becomes converted into a lid or oiierculuni which is 

 sometimes drawn out into a projecting tip. At the margin of the op>erculum a 

 narrow iione of epidermal cells termed the ring or .\nnulus becomes specially 

 differentiated. The cells of the anuulus contain mucilage, and liy their expansion 

 at maturity assist in throwing off tlie lid. In "most stegocarpous Mosses the 



cin 





Fig. 38.5. — Mnkun horninn. Median longi- 

 tudinal section of a lialf-ripe sporogonium. 

 o, OpeicuUuii ; p, peristome ; c, columella ; 

 s, spore-sac containing tlie spores ; i, air- 

 space ; lip, apopli ysis ; s/, st.oniata. ( x 18.) 



Fic;. 3StJ. — Mniumhurnuin. Transverse .section 

 tlirougli the wall of the capsule in the region 

 of the ring, a, Cells of the ring ; 1-/,, succes- 

 sive cell layers witli the thickened masses of 

 the peristome, d', d" ; d"', transverse pro- 

 jecting ribs; c, the coalesced cilia, (x 

 •240.) 



mouth of the dehisced capsule bears a fringe, the pekistome, consisting usually 

 of tooth-like ajipendages. 



The peristome of T^iT/iiiMii honmm (Fig. 387), which will serve as an example, 

 is double ; the outer peristome is formed of 16 pointed, transversely striped teeth 

 inserted on rhe inner margin of the wall of the capsule. The inner peristome lies 

 just within the outer, and consists of cilia-like appendages, which are ribbed on 

 the inner side and tlius appear transversely striped ; they coalesce at their base into 

 a continuous membrane. Two cilia of the inner peristome are always situated 

 between each two teeth of the outer row. 



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

 portions of the opposite Avails of a single layer of cells next to the operculum (Fig. 



