358 



MUSCINEM. 



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, in lit.). 



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 



Fig. 244. — Diagram of the branching of those 

 Jungermannieae in which lateral shoots take the 

 place of the ventral lobe of the dorsal leaves; 

 B, ventral surface (after Leitgeb). 



Fig. 245. — Inflorescence of Raeiitla cotn- 

 pianata ; ar archegonium ; an antheridium ; 

 b leaf (after Hofnieister). 



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 quad- 

 ripartite, as in Tricbocolea, 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 Jneiira 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 v^^hat follows with respect to Mosses. 



^ What follows is partially derived from I^eitgeb's letters. [See his Unteisuchungen, III.] 



