150 



LYCOPODIALES 



[CH. 



parenchyma containing scattered groups of tracheae (fig> 

 169, A, xy. 



Fig. 169, A, is a diagrammatic sketch of the tissues — 1 mm. 

 wide- — between the primary xylem x, and the inner cortex. 

 The primary xylem is succeeded by short parenchymatous cells 

 followed by a zone of radially elongated elements passing 

 occasionally into rows of narrow scalariform tracheae, some of 

 which, owing to their sinuous longitudinal course (fig. 171, C), 

 are seen in oblique section, as at C, tig. 169, A. At its outer 

 edge this secondary tissue, x^, consisting of parenchyma and 

 tracheae, passes into the cambial band (fig. 169, B, a). 



Fig. 170. Lepidodendroii fuliginosum. (From sections in the Manchester 

 Museum.) 



The radial longitudinal section represented in fig. 168, C, is 

 taken from the fossil described by Weiss as a biseriate Halonia ; 

 it agrees sufficiently closely in structure with others referred to 

 Lepidodendroii fuliginosum to be classed as an example of this 

 anatomical type. A complete transverse section of the stem 

 measures 9x6'3cm.; the breadth of the tissues between the 

 edge of the primary xylem and the outer edge of the secretory 

 zone is 2'5 mm. The middle cortical region, characterised by 

 the sooty appearance, which led Williamson to choose the 

 specific n-Avae fuliginosum, is traversed by the leaf- traces and is 

 sharply differentiated from both the inner and outer cortex. 



1 As Miss Stokey (09) points out the production of parenchyma internal 

 to the cambium of L. fuliginosum is a feature shared by Isoetes. See also Scott 

 and Hill (00), p. 424. 



