Cavers: N'ofes oti Yorkshire Bryophyfes. 331 



this cell three sets of segments are cut off, the ventral segments 

 giving rise to the axial portion of the stem, with the rhizoids 

 and scales, whilst the lateral segments give rise to the leaves 

 and to the lateral wing on which the leaves are carried, as well 

 as to the sexual organs. Each lateral segment shows at an 

 early stage a division into an upper portion which gives rise 

 to a leaf and a lower portion which contributes to the formation 

 of the expanded wing of the stem. Each ventral scale arises as 

 a club-shaped mucilage-hair, boine on a stalk-cell which soon 

 divides actively and forms a narrow plate of cells ; the original 



o o 



Fig. 4. — I. Longitudinal section through apex of stem, showing the tuberous swell- 

 ing (T.) behind and below the growing-point (G.P.). II. Transverse section of 

 growing-point, showing the apical cell (X.). On either side are the young leaves 

 (L.); below are two mucilage-hairs in cross-section. III. Part of a longitudinal 

 section through the growing-point. L., leaves ; JM.H., mucilage-hairs. IV. Two 

 cells in the tuber, showing densely granular contents. I., x 20; II., III., x 150; 

 IV.. X 350. 



mucilage-hair is carried out on the apex of this plate, the 

 marginal cells of which also grow out to form similar hairs 

 (Fig. 4, II., III., M.H.). 



Lindberg,* in a brief note on Petalophylliim, suggested that 

 the lamellae, together with the lateral expansion bearing them, 

 arise by the fusion of overlapping leaves, and that only the thick 

 median portion of the shoot is to be regarded as the stem, but 

 careful examination of the plants by means of sections, especially 



* Manipulus Muscoriim seciindiis, 1874, p. 390. 



1903 September i . 



