F. Cavers. 
278 
of this organ occurs independently of fertilisation, though it probably 
does not reach mature size if no archegonia have been fertilised. 
The perianth is by most writers regarded as a structure formed by 
the fusion of the uppermost leaves (two or three in number according 
to the species) of the female axis. In many cases, the form of the 
mature perianth certainly supports the view that it corresponds to 
concrescent leaves, the orientation of which agrees with that of the 
ordinary vegetative leaves of the species. The union of two leaves 
and an underleaf, all remaining flat, gives a perianth of the 
“ epigonanthous ” type, having the form of a triangular prism, three 
angles or keels being formed by the united margins of the leaves ; 
one of the flat sides is ventral, one of the keels dorsal—e.g., 
Lopliocolea (Fig. 49, A). A modification of this is seen when no 
under-leaf takes part in the formation of the perianth—the latter 
is compressed laterally—e.g., Plagiochila (Fig. 49, B). When the 
Fig. 49. Diagrammatic transverse sections of four types of perianth in 
Acrogynse. A, is epigonanthous ; C, hypogonanthous; B, compressed laterally ; 
D, compressed dorso-ventrally. 
perianth-forming leaves are folded, instead of being flat, we may 
again get a triangular perianth, but this time the third keel is 
ventral instead of dorsal ; this “ hypogonanthous” type (Fig. 49, C) 
occurs in many genera, e.g., Cephalozia, Bazzania, Lepidozia, Porella, 
Frullania, and the Lejeuneas. When no under-leaf enters into this 
type of perianth, we again have a compressed structure, but this 
time (Fig. 49, D) the flattening is dorsiventral—parallel with the 
substratum instead of at right angles to it (e.g., Scapania, Radula). 
But in many species the form of the perianth does not fall into line 
with these types, and if we support the interpretation that the 
perianth is invariably a foliar structure, it is not easy to account for 
the many cases in which it is devoid entirely of angles or keels ; in 
other cases the interpretation is made difficult by the presence of 
additional keels, which may be without any definite orientation. 
According to Leitgeb (54) the perianth arises from the last segments 
cut from the apical cell before the latter becomes used up in the 
