284 BRYOPHYTA 
Another Cleistocarpic type, but again one of doubtful affinity, is 
Archidium, in which the small sporogonium has been examined develop- 
mentally by Leitgeb.1 The first stages agree with those of the Phascaceae ; 
but the tissue of the endothecium shows no differentiation into archesporium 
and columella: certain few cells of it, definite neither in number nor in 
position, become spore-mother-cells, while the sterile cells in which they 
are embedded are absorbed as the spores become matured. This con- 
dition in Archidium suggested to Leitgeb a comparison with that in certain 
Liverworts, for instance, Rze//a; but in view of the facts ascertained by 
Fic. 140. 
Nanomitrium tenerum. Archegonium after fertilisation and young sporogonium at 
different stages of development, in longitudinal section. In II. the endothecium is 
shaded. #=foot; S=stalk.« IV. Sporogonium showing the sporocytes in greater part 
separate round the columella. All magnified, I. the most highly. (After Goebel.) 
Lang, the comparison with Vofothy/as would seem more pertinent. 
Without suggesting even a remote relationship, these two forms both 
illustrate how individual cells, distributed without order in an otherwise 
sterile columella, are partially fertile; and they suggest that the whole of 
the columella was originally fertile. Of this in the Liverworts there is 
substantial comparative evidence, and this adds probability to the similar 
conclusion for the phylum of the Mosses. 
While it is thus seen that in normal Cleistocarpic forms, which may 
be held to be either primitive or reduced, internal cells of the endothecium 
may develop as spore-mother-cells, a similar condition is also seen 
occasionally in Stegocarpic forms as an abnormality: cases have been 
described of the appearance of fertile cells among the normally sterile 
1 Sits. Akad. Wiss., Wien, 1879. 
