438 



MOSSES AND FERNS 



CHAP. 



T/ie Stem ^ 



A longitudinal section of one of the numerous subterranean 

 buds (Fig. 228) shows that the conical apex of the stem is 

 occupied by a large pyramidal cell whose segmentation is 

 exceedingly regular. The youngest of the foliar sheaths is 

 separated from the apex by several segments, but below, the 

 next older sheath is very close to it, and the internode, which 

 in the older stem is so conspicuous, is scarcely perceptible. 

 The closely-set sheaths grow very rapidly, so that all but the 

 youngest ones extend beyond the stem apex, which is thus 



Fig. 228. — A, Median section of a strong subterranean (vegetative) bud, X30; k, lateral bud! 



B, the apex of the same section, X 200. 



very completely protected. They form a compact, many- 

 layered covering about it, presenting very much the appearance 

 of the leaf-buds of many Spermaphytes. The apical cell shows 

 the usual three series of lateral segments. These are arranged in 

 three rows, but owing to a slight displacement in the younger 

 ones, the teeth of the sheaths alternate. Each cycle of three 

 segments comes to lie practically in the same plane, and con- 

 stitutes a disc which later forms a node and internode of the 

 stem. Each segment is first divided by a wall nearly parallel 

 to the wall by which it was cut off from the apical cell, into 

 two overlying cells. The upper cells or semi-segments give 

 rise to the nodes, the lower to the internodes. 



^ Rees (2) ; Sachs, see Goebel (10), p. 261 ; Janczewski (3). 



