GROUP II. BRYOPHYTA : HEPATIC^. 333 



Adult shoot, generally dorsi ventral ; thalloid in many forms ; 

 has unicellular root-hairs ; no trace of vascular tissue ; leaves 

 (when present) destitute of a midrib. 



Sporophytic Characters. The sporogonium remains within the 

 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 Anthocerotaceae) is a mass of 

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

 Ricciese) 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 Anthocerotacea?). 



Class IV. JViusci (Mosses). 



Gametophytic 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. 



Sporophytic 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, but 

 is a layer of cells (except Archidium) ; the archesporial cells are 

 all sporogenous, none being sterile or forming elaters ; there is 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. HEPATICJ] (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 

 dorsiventral, except in Haplomitrium and some species of Riella 



