152 



LYCOPODIALES 



[CH. 



Lepidodendron shoot. This applies to other species of the 

 genus as well as to L. fuliginosum. 



Fig. 171, A, shows more clearly the broad zone of secondary 

 parenchyma with the thinner- walled cambial region, a; the latter 

 is represented on a larger scale in fig. 171, B. The section 

 shown in fig. 168, D, and in fig. 170, A, affords an example of a 

 stem in which the secondary tissue consists largely of narrow 

 scalariform tracheae, x^ ; the primary stele has a diameter of 

 1 cm. ; the secondary xylem, cc'^, forms a fairly broad zone of 

 parenchyma and tracheal elements through which leaf-traces 

 pass vertically, a fact of some interest in comparison with the 



//— 



Fio. 172. Lepidodendron fuliginosum. From a section (4x3-4 cm.) in the 

 Williamson Collection, British Museum (No. 379), figured by 

 Williamson, Phil. Trans. R. Soc. 1881, PI. 52. 



horizontal course which they pursue through the medullary rays 

 in the normal secondary wood of L. vasculare and L. Wilnschi- 

 anum. The secondary tracheae pass gradually into thin-walled 

 cambial cells (a, fig. 168, D; 170, A) with parallel tangential 

 walls. Fig. 171, C, shows the sinuous course of the secondary 

 tracheae as seen in longitudinal section, and a few small 

 groups of parenchymatous cells, mr, which may be of the nature 

 of medullary rays, enclosed between the winding scalariform 

 tracheae. 



The secretory zone of Lepidodendron fuliginosum agrees 

 essentially with that of other species; it usually presents the 



