BRYOPHYTES 
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. 
