MARCHANTIALES 261 
may be taken as a fair example (Fig. 121), is more complex than that 
of the Ricciaceae in having polarity of structure, and differentiation of 
the internal mass of sporogenous cells. Both these characteristics suggest 
further steps in sterilisation of potentially fertile cells. The polarity is 
marked in the more or less oblong external form, but more definitely 
by the fact that the basal tissue is sterile, and develops as the foot 
i. 
noo. ob. 
NLe.sk. nv, 
Fic, 121. 
Sporogonium of Fegatella (Conocephalus). 1., venter of fertilised archegonium with 
eight-celled embryo. II., transverse section of a similar embryo. III., IV., older em- 
bryos in longitudinal section. V., part of a longitudinal section of a developing capsule, 
showing differentiation of archesporial tissue into elater-forming cells (¢2), and sporogenous 
cells (sf). VI., part of longitudinal section of receptacle with embryo. VII., similar 
section showing two mature sporogonia in outline. a@c=air-chambers; ca/=calyptra; 
caps=capsule ; f=foot ; #=neck of archegonium ; 4=pore; vec. s¢.=stalk of receptacle ; 
rhiz.=rhizoids; s=seta of sporogonium. I.-V.x 360. VI.x76. VII.x20. (After Cavers.) 
which supports the fertile capsule (Fig. 121, vur.). It is stated that the 
whole hypobasal half of the zygote is thus sterile, though this limitation 
may not apply for all cases. This state as compared with that of Azccia 
might be expressed as a consequence of sterilisation of the whole product 
of the hypobasal half of the zygote; but it is still a matter for debate 
whether the Ricciaceae really represent the progenitors of the Mar- 
chantiaceae. The presence of this polarity may be held as a biological 
concomitant of the position of these larger sporogonia relatively to the 
thallus which bears them: the spherical form of Riccia is suitable to its 
