VII 



THE BRYINEyE 



213 



latter, as well as the 

 are characterised by the 

 starch contained in them, 

 as are the narrow cells of 

 the leaf- traces. Other- 

 wise starch is often com- 

 pletely absent from the 

 stem of Polytridnini and 

 is replaced by oil. The 

 latter is abundant, and 

 probably albuminoids as 

 well, in the thin -walled 

 tissue surrounding the 

 central cylinder. In the 

 latter oil is not so abund- 

 ant, as its cells for the 

 most part contain only 

 air." 



The leaf - traces, or 

 continuation of the central 

 tissue of the midribs of 

 the leaves, bend down 

 into the stem, and fin- 

 ally unite with the axial 

 cylinder of the latter, in 

 a manner quite analogous 

 to that found in the stems 

 of many vascular plants. 



Bastit,^ who more re- 

 cently has made a com- 

 parative study of the 

 subterranean and aerial 

 stems of P. juniperinuin, 

 divides the outer tissue 

 of the latter into epi- 

 dermis, hypoderma, and 

 cortex. In the subter- 

 ranean stems he finds the 

 construction quite differ- 

 ent from that of the leafy 



cells lying immediately 



Fig. 107. — A, Transverse section of tlie leaf of Leuco- 

 bryum; B, similar section of the Xftui of Polytrichum 

 comtnttne ; cl, chlorophyll-bearing cells (after Goebel). 



^ Bastit (i), p. 295. 



