318 PART IV. CLASSIFICATION. 



calyptra until the spores are ripe ; the ruptured calyptra remains 

 as a vaginula, no portion of it being raised as a cap on the sporo- 

 gonium ; the elongation of the seta (when present) is sudden ; the 

 growth of the sporogonium is not effected by a two-sided apical 

 cell. 



The archesporium (except in the Anthocerotacese) is a mass of 

 cells co-extensive with the endothecium ; in all cases (except 

 Ricciere) some of the archesporial cells are sterile, being frequently 

 developed into elaters ; a columella is present only in the Antho- 

 cerotacese. 



There is no trace of vascular tissue in the sporophyte, nor are 

 there any stomata in its epidermis (except Anthocerotacese). 



Class IV. Musci (Mosses). 



Gamctophytic Characters. Protonema frequently persistent, 

 well-developed, generally filamentous. Adult shoot, radial or 

 isobilateral ; always differentiated into stem and leaf ; no root- 

 hairs, but branched multicellular rhizoids ; stem frequently with 

 a central strand of rudimentary vascular tissue ; leaves generally 

 with a midrib. 



Sporophytie Characters. The sporogonium escapes from the 

 calyptra at an early stage ; a portion of the calyptra (with certain 

 exceptions) is carried up as a cap on the sporogonium ; the elonga- 

 tion of the seta is gradual ; the growth of the sporogonium is 

 (except Sphagnacese) effected by a two-sided apical cell. 



The archesporium is not co-extensive with the endothecium, and 

 is generally a layer of cells ; the archesporial cells are all sporo- 

 genous, none being sterile or forming elaters ; there is usually 

 a well-developed columella in the capsule. 



The seta frequently has a central strand of rudimentary vascular 

 tissue ; the epidermis of the capsule is generally provided with 

 stomata. 



Class III. HEPATIOE (Liverworts). 



A. The GAMETOPHYTE. The spore gives rise, on germination, 

 to a small protonema which is sometimes filamentous, but more 

 generally a flattened cellular expansion. 



The Adult Shoot springs from the protonema. Its symmetry is 

 generally dorsiventral. It is commonly thalloid, but is differ- 

 entiated into stem and leaves in some forms (e.g. foliose Junger- 

 manniacese). Its growth is effected by an apical growing-point in 



