Acrogynous Jungermanniales. 279 
formation of the archegonia. We have seen that vegetative leaves 
may undergo concrescence, and in some cases this occurs with the 
leaves (bracts) of the involucre. The perianth may be absent 
altogether—a condition especially found in species having a fruit- 
sac or marsupium. 
In its fully-developed form, the marsupium is a tubular structure 
which grows downwards into the substratum, bearing rhizoids on 
its outer surface, while the young sporogonium develops inside it 
at the closed lower end, and the ripe capsule is thrust out of its open 
upper end when the seta elongates. The development of the 
marsupium has been investigated by Gottsche (34, 35) and by 
Leitgeb (57), and more recently by Goebel (32, 33) and by Douin (7). 
All the species possessing this remarkable structure were until 
recently classed together as an independent family, the “Geocalyceae,” 
but this is an entirely artificial group, the marsupial genera and 
species being scattered over four of the eight families of Acrogynae 
now generally recognised. The independent origin of the marsupium 
in unrelated genera, and in certain species of otherwise normal 
genera, forms one of the most striking examples of homoplasy to be 
found even in the Hepaticae. Moreover, the marsupium has clearly 
arisen in several different ways in different cases, as we shall 
presently see. 
The whole subject of the arrangements for the protection and 
nutrition of the developing sporogonium has never received the 
detailed consideration which it deserves, though these arrangements 
appear to be of great importance in connexion with the phylogeny 
of the Acrogynae. In the simplest case, typical of the majority of 
the Acrogynous genera, the young sporogonium is invested by (1) 
the calyptra formed from the venter of the fertilised archegonium, 
(2) the perianth, which arises as a ring-like outgrowth around the 
archegonial group, and which is doubtfully regarded as a concrescent 
leaf structure, and (3) the involucre of more or less modified leaves 
—all these envelopes being free from each other, while the foot, or 
enlarged base of the sporogonial seta, is embedded in the base of 
the calyptra (Fig. 50, I.). 
The writer has investigated the morphology of the sporogonial 
envelopes in species belonging to the majority of the genera of 
Acrogynae, and has found that in nearly half of the genera (excluding 
the Lejeuneaceae), there are indications of stages leading up to 
the fully developed marsupium of the “Geocalyceae.” Starting 
from the simplest condition in which the three envelopes—calyptra, 
