368 PART III. THE CLASSIFICATION OF PLANTS. 



apophysis in some forms (e.g. Splachnum, Po'ytric.hum"). Part of the external 

 layer of the endothecium becomes the archesporium, which forms a hollow 

 cylinder round the columella, but does not extend over the top of it : an air- 

 chamber is developed in the amphithecium round the spore-sac, and is gener- 

 ally traversed by strands of cells (containing chloroplastids) stretching from the 

 wall of the capsule to the spore-sac. In the lower forms the capsule is either 

 indehiscent, its wall becoming eventually disorganised, or it ruptnrt-s irregu- 

 larly ; in the higher forms, the apical portion of the wall is thrown off as au 

 operculum, and a peristome is generally developed round the aperture thus 

 formed. In all cases a portion of the calyptra is carried up as a cap on the 

 top of the developing sporogonium. 

 The Bryineaa are classified as follows : 



Tribe I. Cleistocarpae. Tribe II. Stegocarpae. 



Tribe I. CLEISTOCAKPJS. The adult shoots are generally minute, un- 

 branched, annual, and always acrocarpous ; there is generally a central strand 

 in the stem, and a mid-rib in the leaf. 



With regard to the sporogonium, the seta is generally short, sometimes ex- 

 panded at the base into a false (epibasal) foot (e.<j. Phascum, Ephemerum), 



without any central strand in some forms. 

 The capsule does not open by means of an 

 operculum, nor has it any peristome (a rudi- 

 mentary operculum can be detected in As- 

 tomum, Mildeella, and a few other forms, as 

 also a rudimentary peristome in Mildeella) ; 



it either ruptures irregularly, or the wall 

 FIG. 250.-a Ephemerum seratnm . d 



( x 3) : b shoot of Andreasa nivalis, 

 with (K) capsule (aat. size). The following are the principal families 



and genera of the Cleistocarpae : 



Fam. 1. Ephemeracece : Ephemerum (Fig. 249 A), Nanomitrium. 

 ,, 2. Physcomitrellacece : Physcomitrella. 

 ,, 3. Phascacea : Phascum, Acaulon, Mildeella, Astomum. 

 ,, 4. Bruchiacece : Pleuridium, Bruchia. 



,, 5. Voitiacece : Voitia, by far the largest forms in tbe tribe. 

 Tribe II. STEOOCABP^E. The characteristics of this tribe are to be found in 

 the sporogonium, which is distinguished by the formation of an operculum and, 

 generally, of a peristome. 



The operculum is developed from the apical portion of the capsule, either 

 from the epidermis alone (e.y. Georgiacese), or from it and one or more of the sub- 

 jacent amphithecial layers. The cell-walls become cuticularised and assume <i 

 yellow or brown colour. The outline of the operculum is circular ; its form 

 cap-like, more or less flattened in some cases, more or less conical in others, 

 sometimes apiculate. 



The limit between the developing operculum and the rest of the capsule 

 (urn) is generally marked by a slightly prominent zone, consisting of one or 

 more rows of rather large epidermal cells, with cuticularised outer wall?, 

 termed the ring or annulus : its position is just above the level of the top of the 

 spore-sac and of the air-chamber. 



The peristome is developed within the operculum, from the innermost layer 



