470 



MOSSES AND FERNS 



CHAP. 



or not. According to Janczewski, certain of these rhizogenic 

 buds of the rhizome produce several roots, but the buds remain 

 otherwise undeveloped. In the aerial stems the roots remain 

 normally undeveloped, but may often be stimulated into growth 

 by keeping the stem moist and dark. 



Van Tieghem ((5), p. 551) describes the roots of E. palus- 

 tre as being exogenous, and says they can be traced to a definite 

 cell of one of the young segments. Janczewski ((3), p. 89), 

 however, was unable to recognise the young root until the first 



Fig. 274. — A, Longitudinal section of the root apex, X200; x, x, the large central ves- 

 sel of the vascular bundle; B, C, two transverse sections passing through the apex, 

 X200. In C is shown the first divisions of the cap cell. 



foliar sheath was well developed, and in E. telmateia I could see 

 no trace of the root in still older buds, and they were apparently 

 always of endogenous origin, although this point was not spe- 

 cially investigated. 



The structure of the apical meristem is much like that of 

 the leptosporangiate Ferns, the main difference being the greater 

 development of the root-cap, in which periclinal walls are fre- 

 quent, so that the older layers, especially in the middle, are 

 several cells thick, and not clearly limited. 



After the sextant walls are formed, each semi-segment is 



