F. Cavers. 
284 
found also in some other species of Nardia and in Notoscyphus, 
Gyrothyra, Prasanthus, and a few other genera. In these forms a 
perianth is usually still present, but it disappears in Prasanthus, and 
it rarely occurs in the more fully developed marsupia—obviously 
because it is no longer required, the protection of the sporogonium 
being taken over by the marsupium itself. The highest development 
of the solid type of ventral marsupium is found in the genera Tyli- 
manthus, Marsupidium, and Marsupellopsis. 
In the Acrobolbus type, which includes the majority of the 
marsupial Acrogynae, the marsupium is tubular from the beginning, 
as compared with the solid Tylimanthus type, but transitions occur 
between the two types. In the Tylimanthus type the archegonial 
group shows dorsiventral symmetry, the archegonia being developed 
only on the dorsal side of the stem, and the marsupium is formed 
by active growth of the underlying tissue. In the Isotachis type the 
archegonial group shows radial symmetry, the archegonia being 
produced all round the apex of the erect stem, and the marsupium 
arises as a ring-like outgrowth of the stem-tissue. In the develop¬ 
ment of the Acrobolbus type, we have a combination of the conditions 
seen in the Tylimanthus and Isotachis types. The archegonial group 
is either developed on the upper half of the stem to begin with, or 
is displaced to the upper side by the grow'th of the ventral tissue. In 
either case, after fertilisation has occurred, this ventral tissue grows 
downwards, forming a cup which becomes extended to produce a 
tube, into the thickened lower end of which the sporogonial foot is 
plunged. In Arnellia, the marsupium begins in much the same way 
as in Nardia geoscypha, but the ventral swelling formed at the end 
of the archegonial branch becomes a shallow cup, to the bottom of 
which the archegonial group is carried, the calyptra remaining free 
right to the base of the cup, while the perianth and involucre are 
left at the mouth ; growth is soon arrested, and the marsupium 
remains in this incipient stage. In Harpanthus, a similar cup-like 
marsupium is formed, but the calyptra is adnate to the inner surface 
of the cup ; in Adelanthus, both calyptra and perianth are carried 
down into the short marsupium. Finally, in the genera Acrobolbus, 
Calypogeia, Lethocolea, Symphyomitra, Kantia, Saccogyna, and 
Balantiopsis, we get well-developed tubular marsupia, sometimes 
reaching a length of several centimetres and completely investing 
the mature sporogonium. In some cases the meristem at the base 
of the developing marsupium is covered by inactive tissue which, as 
Goebel has pointed out, resembles a root-cap in structure and 
