HEPA TIC JE. 
359 
serve to explain this remarkable process, where the apical view of a branching shoot is 
represented diagrammatically : I, II ... FI are the segments of the apical cell S of the 
primary shoot ; //, F being segments of the ventral, /, ///, IF, FI of the dorsal side. 
The two segments / and /// are already divided by a longitudinal wall each into two 
halves respectively dorsal and ventral ; and in the latter the apical cell s of each lateral 
shoot has already been constituted by the formation of the walls i, 2, 3, while the dorsal 
half of each of these segments has developed into half a leaf. The other segments which 
do not form shoots develope normal two-lobed leaves. This is the process that occurs in 
Frullania, Madotheca, Mastigobryum, Lepido%ia, Trichocolea, and Jungermannia trichophylla. 
A third type of branching occurs finally in Radula and Lejeunia, where the formation of 
leaves is not disturbed by the branching, the branches springing from behind the leaves at 
their base, and from the same segments. 
Besides these modes of ramification of the segments of definite position, Leitgeb has 
recently discovered an endogenous formation of shoots, which are sometimes fertile 
branches, from the ventral segments provided with amphigastria, e.g. in Mastigobryum, 
Lepido%ia, and Calypogeia ; or they are formed without the production of a ventral row 
of leaves, as in Jungermannia bicuspidata and other Jungermannieae with leaves in two 
rows. In those especially which belong to the section Trichomanoideae the fertile 
branches are developed thus, and break out from the older parts of the stem as adven- 
titious shoots ; probably, however, their mother-cells always originate regularly in 
acropetal succession in the primary meristem of the vegetative cone, as in Mastigobryum 
and Lepidozia, but their development is deferred. Finally according to Leitgeb, the 
whole branching of many Jungermannieae appears to depend exclusively on the pro- 
duction of branches in this manner. 
The reproductive organs are distributed monoeciously or diceciously, and are formed, 
in the thalloid genera, on the dorsal side of the shoot \ in the foliose Jungermannieae at 
the end of primary shoots or of special small fertile branches, which commonly have the 
above-described adventitious origin on the ventral side. The antheridia are usually in 
the axils of the leaves, singly or in groups. The archegonia appear generally in large 
numbers at the summit of the shoot, either on those which bear antheridia below, or 
on special branches, which in the Geocalyceae are hollowed out in such a manner that 
the archegonia are sunk in a deep pitcher-shaped hollow, an arrangement which may be 
compared, to a certain extent, with the structure of a fig. This occurs in an especially 
striking manner in Calypogeia. Where this peculiar enveloping of the archegonia does 
not occur, they are concealed by the nearest leaves (the perichaetium) ; and a perigynium 
is usually formed in addition, which grows round the archegonia as a special membranous 
envelope. The development of these organs has been accurately described by Leitgeb 
in the case of Radula complanata (Fig. 245). The primary and lateral shoots both bear, 
as a rule, both kinds of reproductive organs; such a shoot is always at first purely 
vegetative, but forms after a time antheridia, and finishes with the archegonia. Less 
often, however, it again recurs, after the production of antheridia, to a vegetative 
development. The antheridia of Radula are metamorphosed trichomes ; they stand 
singly in the axils of the leaves, and are completely enclosed in the hollow formed by 
the very concave lower lobe of the leaf. They arise from the club-shaped protuberance 
of a cell belonging to the cortex of the stem and lying before the leaf at its base. 
The archegonia of Radula always stand at the end of the primary or of a lateral shoot, 
from three to ten together, surrounded by a perigynium, which is again enveloped by a 
perichaetium of two leaves. 1 he archegonia together with the perigynium are de- 
veloped from the apical cell of the shoot and from its three youngest segments. The 
archegonia arise from the apical cell itself, and from the upper parts of its lateral 
^ In Metzgeria furcata the antheridia and archegonia make their appearance diceciously on the 
concave dorsal surface of adventitious branches which arise from the ventral surface of the mid-rib 
and are so curved as to enclose the sexual organs. (^Leitgeb.) 
