GROUP II. BRYOPHYTA : HEPATIC^. 325 



generally a row of amphigastria on its ventral surface. In the radial 

 foliose forms, the leaves are borne in three rows in Haplomitrium, and in 

 two rows in the radial species of Riella; here there is no distinction of 

 amphigastria. 



The growth of the shoot is effected by an apical growing-point which 

 possesses a single apical cell. The apical cell of the thalloid forms is most 

 commonly two-sided (Fig. 200) ; the base is directed outwards, the apex 

 inwards, and from the two sides segments are cut off alternately right 

 and left. But in Pellia the cell is bounded by four surfaces an external 

 free surface, an internal, and two lateral ; segments are successively cut 

 off along the internal and the two lateral surfaces. The apical cell of the 

 foliose forms, with the exception of Fossombronia and Riella which have 

 a two-sided apical cell, is a three-sided pyramid; its base is directed out- 

 wai-ds, its apex inwards, one side is ventral and the other two are dorso- 

 lateral ; this latter statement does not, of course, apply to Haplomitrium, 

 which is radial. 



The normal mode of branching in the dorsiventral forms is that which 

 takes place at the growing-point in the plane of expansion. In the thal- 

 loid forms, as also in the foliose Fossombronia and Blasia, it may be 

 described as dichotomous (see p. 132) although the apical cell does not 

 undergo division so as to form the apical cells of two branches ; the apical 

 cell of the parent shoot persists, and that of the branch is developed from 

 an adjacent segment, either before or after further division. When the 

 two shoots develope with equal vigour, the resulting branch-system re- 

 sembles a dichotomy ; but when the parent shoot grows the more vigor- 

 ously throughout, the branches are lateral upon it and the branch-system 

 is a monopodium (see p. 19). In the foliose forms the mode of normal 

 branching is generally monopodial. The apical cell of a lateral branch is 

 developed from the lower (ventral) half of a dorso-lateral segment cut off 

 from the apical cell ; either from the whole of the segment, or from the 

 posterior (basiscopic) portion of it. 



In some of these plants there is a formation of gemmx. In Aneura 

 certain cells of the margin and of the dorsal surface of the shoot each 

 become divided into two, anl the two cells thus formed are set free as a 

 bicsllular gemma, with probably a proper wall of its own, by the rupture 

 of the enclosing wall. In Blasia, the gemmae, which are solid multicellular 

 nearly spherical bodies, are developed in special receptacles (cupules) 

 situated on the dorsal surface of the apex ot the shoots ; their mode of 

 origin resembles that of the gemmae of Marchantia. In most foliose forms 

 the gemmae are developed from marginal cells of the leaves (e.g. Jumjer- 

 mannia ventricosa) or from cells near the growing-point of the stem (e.g. 

 .Junyermannia blcuspidala). In these forms the gemmae are usually uni- or 

 bi-cellular, but in Rtdula complanata (where they are formed on the leaf- 

 margin) they are flat multicellular plates of tissue. 



The leaves are developed, generally speaking, one from each segment 

 formed from the apical call. In the typical Acrogynae each dorso-lateral 

 segment gives rise to a lateral leaf, and each ventral segment to a ventral 

 leaf (amphigastrium) ; though, as alread3 r mentioned, the amphigastria 



