:^oH MUSCINE.E. 



parallel to one another and to the axis of growth of the stem\ In the species with 

 leaves arranged in two rows a leaf springs from each of the lateral and dorsal seg- 

 ments; when the leaves are arranged in three rows each segment of the ventral side 

 also produces a leaf, w^hich is however smaller and of simpler structure and is also 

 inserted transversely, while the insertion of the dorsal row of leaves is oblique to the 

 axis of the stem, so that the lines of insertion of each pair form an acute angle. Before a 

 lateral segment has developed a papilla from which the leaf is formed, it divides by a 

 longitudinal wall into an upper and a lower half facing dorsally and ventrally, each of 

 which now forms a leaf-papilla. Hence it arises that the leaves of Jungermannieae are 

 to a certain extent bisected or two-lobed ; in the simpler leaves this is usually shown 

 by a more or less deep incision of the anterior margin ; but even when the leaves 

 are quadripartite, as in Trichocolea, the primitive double origin can still be recognised. 

 The lower lobe of the leaf is usually smaller, of peculiar form, and hollowed out. 



The branching of the growing end of the shoot in the case of Metzgeria has already 

 been represented in Fig. loo (p. 120). According to Leitgeb it takes place in a similar 



manner also in the other thalloid forms with a 

 wedge-shaped apical cell, viz. in Aneura and Fos- 

 sombronia. The very variable relation of the 

 branching to the leaves discovered by Leitgeb ^ is 

 especially remarkable. In Metzgeria and Aneura 

 no leaves, but only branches, are formed out of 

 the segments ; in Fossombronia the lateral shoot 

 springs from the segment in place of a whole 

 leaf; on the other hand, in the greater number 

 of Jungermannieae with filiform leafy stem and 

 three-sided apical cell, the lateral shoot springs 

 from the segment in place of the lower or ventral 

 lobe of the leaves of the dorsal side, so that in 

 these cases the branch may be considered as a 

 metamorphosed half-leaf. Fig. 223 will serve to 

 explain this remarkable process, where the apical 

 FIG. 223.-Diag:ramofthe branching of those jun- ^jg^^ ^f ^ branching shoot is represented dia- 



germanniere m which lateral shoots take the place '-' ^ 



of the ventral lobe of the dorsal leaves (after grammatically : I, 11 ... FI are the scgmcuts of 

 ^' ^^ ■ the apical cell S of the primary shoot ; II, V 



being segments of the ventral, /, III, IF, FI, 

 of the dorsal side. The two segments / and /// are already divided by a longitu- 

 dinal 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, Lepidozia, 

 Trichocolea, and Jungermannta trichophylla. A third type of branching occurs finally in 

 Radula and Lejeunia, where the formation of leaves is not disturbed by the branch- 

 ing, the branches springing from behind the leaves at their base, and from the same 

 segments. 



Besides these modes of ramification, which originate from particular outer cells 

 of the segments of definite position, Leitgeb has recently discovered also an endogenous 

 formation of shoots, springing sometimes as fertile branches from the ventral segments 

 provided with amphigastria, while the exogenous shoots arise in the manner represented 

 in Fig. 223, as, e.g. in Mastigobryum, Lepidozia, and Galypogeia ; or they are formed 



^ Compare in reference to this what follows with respect to Mosses. 

 ^ What follows is partially derived from Leitgeb's letters. 



