122 
F. Cavers. 
between a caducous adventive shoot and a gemma, these types 
being connected by intermediate forms. 
It will be convenient to deal first with the methods of propa¬ 
gation which have been actually observed in nature, taking the 
families of Hepaticae in turn, and afterwards to describe the 
processes of regeneration observed when the plants are cultivated 
and experimented with in the laboratory, under various conditions 
that differ more or less from those under which the plants grow 
naturally. The two sets of phenomena, which we may distinguish 
as natural and induced respectively, in some respects coincide, 
whilst the facts obtained by experiment often throw light on 
those observed in the field and lead to certain generalisations and 
conclusions which will be discussed later. 
Naturally-Occurring Organs of Asexual Reproduction. 
I. Marchantiales. In this group, asexual reproduction is 
chiefly carried on by the dying away of the older parts of the 
branched ribbon-like thallus and the liberation of the ordinary 
branches, or by means of adventive branches, though in some cases 
(Marchantia, Lunularia , Fegatella) specialised gemmae are produced. 
Fam. I. Riccioideae. Very common in this family is the 
formation of adventive branches, which arise from the ventral 
surface of the thallus, ultimately becoming detached. In Ricciella 
jluitans , the sterile form of which occurs floating on water or 
submerged a little below the surface, the formation of these 
branches is often so abundant that the plants cover a sheet of 
water in much the same manner as Duckweed. In Ricciocarpus 
natans , the broad heart-shaped thallus after repeated branching 
often becomes split longitudinally, each half giving rise to a 
separate plant. This splitting occurs regularly in fertile plants and 
results in the rupture of the embedded capsules and the shedding 
of the spores. In several species of Riccia which inhabit dry regions, 
e.g ., R. vesicata, perennis , bulbifera, the plant produces special 
ventral branches, each of which becomes swollen up terminally and 
forms a tuber. These tubers, the tissue of which contains reserve 
food materials, chiefly in the form of oil-drops and proteid grains, 
are adapted for enduring a dry period, afterwards giving rise to 
new shoots. 
Fam. 2. Corsinioideae. In the two genera included here, 
Corsinia and Boschia , adventive branches are occasionally formed, 
as in the Riccioideae. 
