330 MOSSES 



ment of the tissues. The stem is formed externally of sclerenchyma 

 (scl), and contains an axial bundle (ax. b) : in some of the leaves (/) 

 the section passes through the midrib, in others (7 1 ) through the lateral 

 portion : the stem ends distally in an apical cell (ap. c), from which 

 segmental cells (seg. c) are separated. 



D, transverse section of the stem of Bryum rosettm, showing scleren- 

 chyma (scl), axial bundle (ax. b). and rhizoids (r/i). (X 60.) 



E, transverse section of a leaf of Funaria, showing the midrib (md. r) 

 formed of several layers of cells, and the lateral portions one cell thick. 

 (X 150.) 



F, small portion of the lateral region of the same, showing the form 

 of the cells and the chromatophores (chr). (X 150.) 



G, distal end of the stem of Fontinalis antipyretica in vertical section, 

 showing the apical cell (ap. c) giving rise to segmental cells (seg. c), 

 which by subsequent division form the segments of the stem with the 

 leaves : the thick lines show the boundaries of the segments. 



H, diagram of the apical cell of a moss in the form of a tetrahedron 

 with rounded base abc and three flat sides abd, bed, acd. 

 (D after Sachs ; G after Leitgeb. ) 



The plant consists of a short slender stem (Fig. 81, A, st\ 

 from which are given off structures of two kinds, rhizoids or 

 root-hairs (r/i), which pass downwards into the soil, and leaves 

 (/), which are closely set on the stem and its branches. As 

 in Nitella (p. 206) the portion of the stem from which a leaf 

 arises is called a node and the part intervening between any 

 two nodes an internode, while the name segment is applied 

 to a node with the internode next below it. At the upper or 

 distal end of the stem the leaves are crowded, forming a 

 terminal bud. 



Owing to the opacity of the stem its structure can only be 

 made out by the examination of thin sections (c and D). It is 

 a solid aggregate of close-set cells which are not all alike but 

 exhibit a certain amount of differentiation. In the outer 

 two or three rows the cells (sd} are elongated in the direction 

 of length of the stem, so as to have a spindle-shape, and their 

 walls are greatly thickened and of a reddish colour. They 

 thus form a protective and supporting tissue to which the 

 name sclerenchyma is applied. Running longitudinally 



