36 Fanner . — Studies in Hepaticae: 
to conceive of the posterior almost wingless portion developing 
as a rhizome, whilst the expanded branch-system would form 
a ‘ frond.’ This distinction into stipe and 4 lamina ’ is actually 
met with in some species, e. g. P . pisiformis , where, to judge 
from herbarium specimens, the stipe forms a creeping stem, 
passing gradually into the ‘ lamina.’ But this morphological 
differentiation of external form culminates in those species of 
which P. decipiens may be taken as an example. 
In this plant there is a well marked creeping subterranean 
rhizome, from which arise expanded stalked aerial ‘ fronds ’ 
or dichotomous branch-systems. In luxuriant specimens, 
especially when dried, the general appearance strongly recalls 
that of some of the simpler Hymenophyllums, but in the 
fresh, living state, its succulent and turgid character forms 
a very striking and distinctive feature. It closely approxi- 
mates in vegetative structure to many species of another 
genus of Hepatics, Symphyogyna , although it is readily dis- 
tinguishable from them by the character of its fructification. 
It is a fact worthy of mention, that within the limits of the 
genus Symphyogyna itself, much the same sort of transition 
from a simpler to a more complex type of vegetative structure 
may be traced. This latter genus has however outstripped 
P allavicinia, in this respect, since it also exhibits considerable 
diversity in the directions of its complexity. Thus, besides 
exhibiting a gradual advance along lines parallel with those 
already indicated as occurring in P allavicinia, in other groups 
of species the thallus becomes deeply indented, so as to 
become pinnatifid (S. sinuata ), and so much so as to almost 
resemble one of the pseudo-foliose genera. It is however 
interesting to notice that on the same plant branches may 
arise whose margins are in no way sinuate, but resemble those 
of any common form in their regular outline ; and on the other 
hand it is perhaps not improbable that in the toothed margins 
to be met with in some Pallavicinias, there is represented 
a rudimentary stage of that development which gives such 
a striking appearance to Symphyogyna sinuata. 
Moreover there are a number of other genera which used to 
