BRYOPHYTES 



105 



an archegonium initial. The neck canal cells are six or eight in number, 

 and the neck is almost as broad as the venter. 



The two kinds of sex organs may occur upon the same plant 

 (monoecious) or upon different plants (dioecious). 



Sporophyte. The sporophyte (sporogonium) is as described for the 

 Anacrogynae (see p. 103), with a conspicuously elongated seta, the same 

 reduction of sporogenous 

 tissue, and the capsule 

 dehiscing by four spread- 

 ing valves (fig. 235). 



Conclusions. The es- 

 sential contrasts between 

 Jungermanniales and 

 Marchantiales may be 

 stated as follows: In 

 Marchantiales there is 



(1) a differentiation of 

 the tissues of the gameto- 

 phyte, but no special 

 differentiation of form, 



(2) less sterilization of 

 potentially sporogenous 

 tissue, (3) little or no 

 development of the seta, 

 and (4) irregular dehis- 

 cence of the capsule. In 

 Jungermanniales there is 

 (i) a differentiation of 

 the gametophyte into 

 axis and leaves, but little 



or no differentiation of tissues ; (2) greater sterilization of potentially 

 sporogenous tissue ; (3) strong development of the seta ; and (4) a 

 definite dehiscence of the capsule by four spreading valves. The two 

 groups differ also in the method of development of the antheridium. 

 In the main, the archegonia of the two groups are similar, the axial 

 row including six or eight neck canal cells (the exceptions being Riccia 

 with four and Sphaerocarpus with two). The archegonium is a very 

 persistent (" conservative ") structure, but the gradual disappearance 

 of the neck canal cells is one of the conspicuous facts in its very slow 



FIG. 236. Porella : portion of antheridial branch 

 showing two axillary antheridia. 



