HEPA TICM. 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 ; II, 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, 

 Lepidozia, 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 Lepido%ia, 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 dioeciously, and are formed, 

 in the thalloid genera, on the dorsal side of the shoot ^, in the foliose Jungermanniege 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. The 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 dioeciously 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.) 



