114 LYCOPODIALES [CH. 



secondary xylem they bend suddenly upwards and for a time 

 follow a steep and almost vertical course. 



In well-preserved longitudinal sections the outermost 

 secondary xylem tracheae are seen to be succeeded by a few 

 narrow and vertically elongated elements (fig. 149, A, a), 

 which represent young unlignified tracheae : these are followed 

 by shorter parenchymatous cells (m) forming part of a meriste- 

 matic zone from which the secondary xylem receives additions. 



Returning to fig. 148, A; the zone of secondary wood, a?, 

 composed of scalariform tracheids and medullary rays, is suc- 

 ceeded by a few layers of parenchymatous cells and beyond this 

 is a broader zone, sc, to which the term secretory zone has 

 been applied*; this is made up of small parenchymatous cells 

 varying in size and of larger spaces which appear to have been 

 formed by the disorganisation of thin-walled elements. The 

 whole zone presents a characteristic appearance due to the 

 association of small cells, large clear spaces, and a certain amount 

 of dark-coloured material suggestive of tissue disorganisation 

 and secreted products. The anatomical characters of the 

 secretory zone are shown in the photograph, fig. 168, A, sc. 

 Several leaf-traces are seen in transverse section in the secretory 

 zone (black dots in fig. 148, A, sc\ fig. 154, C, li)\ each trace 

 consists of a strand of narrow tracheae accompanied by a few 

 encircling layers of small parenchymatous cells. As a trace 

 continues its steeply ascending course through the secretory zone, 

 it becomes associated with a strand of that tissue and assumes the 

 form of a collateral vascular bundle, the outer part of which does 

 not consist of typical phloem but of shorter elements derived 

 from the secretory zone. Beyond the secretory zone we find a 

 more homogeneous tissue composed of parenchymatous elements 

 slightly extended tangentially (figs. 148, A, c'; fig. 168, A, c); 

 this is spoken of as the inner cortical region. In the great 

 majority of sections of L. vasculare as of other species of the 

 genus, the broader middle cortex (fig. 148, c^) is occupied by 

 mineral matter, introduced subsequent to decay of the tissue ; 

 or it is represented by patches of delicate tissue composed of 

 loosely arranged parenchymatous cells varying considerably in 



1 Seward (99) p. 144. 



