358 
MUSCINE^. 
forming segments by walls inclined alternately upwards and downwards (towards the 
dorsal and ventral surfaces), as well as lateral segments from which the leaves proceed ; 
a leaf is produced from the dorsal part of a lateral segment, a kind of leaf-tube from its 
central part, and a second leaf from its ventral part, though this last is more often 
absent' (Leitgeb, //V.). 
In the Jungermannieae with filiform stem and leaves arranged in two or three 
rows, the stem ends in a three-sided apical cell which forms three rows of segments 
in spiral succession ; two rows being dorsal and lateral, while the third row forms the 
under or ventral side of the stem. The successive septa of each row of segments are 
parallel to one another, and the segments themselves are in straight rows, the rows being 
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 dorso-lateral segments ; 
when the leaves are arranged in three rows each segment of the ventral side also 
produces a leaf, which is however smaller and of simpler structure and is also inserted 
transversely, while the insertion of the dorsal rows 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 longi- 
tudinal 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 Jun5:ermannieae 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 quad- 
ripartite, 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. no. According to Leitgeb it takes place in a similar manner 
also in the other thalloid forms with a two-sided apical cell, viz. in ylneura and Fossom- 
bronia. 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. 244 will 
* Compare in reference to this what follows with respect to Mosses, 
2 \\ hai follows is partially derived from Leitgeb's letters. [See his Untersuchungen, III.] 
R 
Fig. 244.— Diagram of the branching of those 
Jungernianniere in whicli lateral shoots take the 
place of the ventral lobe of the dorsal leaves; 
B, ventral surface (after Leitgeb). 
I'IG. 245. — Inflorescence of Rnditla com- 
planata ; ar archegoniuin ; an antheridium ; 
b leaf (after Hofmeister). 
