186 



LYCOPODIALES 



[CH. 



described by the former author (fig. 190) affords an interesting 

 example of an unusual manner of fossilisation ; a hollow stem oi 

 Lepidodendron is filled with sedimentary material containing 

 several pieces of Lepidostrohi in an approximately vertical 

 position. 



Fio. 190. Lepidodendron stem with Lepidostrohi. (After Hooker.) 



A. Side-view showing leaf-cushions on the left-hand side and the 

 KnoiYia condition on the right. 



B. View of transverse section ; s, sections of Lepidostrohi. 



The fact that Lepidostrohi usually occur as isolated speci- 

 mens renders it impossible in most cases to refer them to 

 particular species of Lepidodendron. Neither external features 

 nor anatomical characters afford satisfactory criteria by which 

 to correlate vegetative and fertile shoots ; in some measure this 

 is due to the imperfection of our knowledge as regards the 

 range of structure within the limits of species ; it is also due 



