Jan. liiOO.] BOTANICAL SOCIETY OF EDlNBUKGll 345 



of the ordinary xylem elements, it is necessary to depend 

 on the abundant protoplasmic contents of the cells as a 

 means of identification, and, in unstained sections, they are 

 only recognisable with difliculty. 



The stem, with its five vascular bundles, is bounded 

 externally by an interrupted circle of isolated sclerenchy- 

 matous fibres, of rectangular, roughly square section, and of 

 considerable length, but which in the young state appear 

 to be only partially lignified, as it is in old stems alone that 

 they give any reaction with phloroglucin or aniline sulphate. 



These fibres are not limited to the regions immediately 

 external to the primary bundles, but in general occur 

 singly at intervals round the stem, though here and there 

 a group of eight or nine may be found united together 

 by their radial walls, in which case the group generally 

 lies on the outer edge of a bundle. Although occasionally 

 thus united side by side, they are seldom duplicated radially, 

 and when this does occur, both elements clearly result from 

 the division of a single mother-cell. 



In longitudinal sections, the outer sieve tubes of the 

 external phloem are readily seen abutting directly on these 

 fibres, which must therefore be looked upon as representing 

 the pericycle, along with the intervening thin-walled cells 

 required to complete the circle, though these latter are in 

 no way specially characterised, and are only distinguishable 

 from those of the succeeding layer by their position 

 and generally smaller size. 



In the majority of young stems this fibrous layer is 

 immediately surrounded by a complete circle of rather 

 large cells, especially rich in starch, which is, however, 

 also to be found in the other cells of the cortex, though in 

 somewhat smaller amount, and although the characteristic 

 dot on the radial walls is apparently absent in the stem, 

 there seems no reason to doubt the identity of this layer 

 with the endodermis. 



The remainder of the cortical tissue, which generally 

 reaches a thickness of from five to ten cells, is composed 

 of rounded, thin-walled parenchyma, often containing 

 traces of starch, and with large intercellular spaces. 



The Boot. — The first indication of the appearance of 

 adventitious roots on S>. Dulcamara takes place at a 



TRANS. BOT. SIIC. EDIN. VOT.. XM. 2 A 



