156 



LYCOPODIALES 



[CH. 



surrounding the imperfectly preserved secretory zone. From 

 the medullated stele a lateral branch, b, is being given off; its 

 crescentic form becoming changed to circular as it passes nearer 

 to the surface. 



A type of Lepidodendron, L. Hickii, founded on anatomical 

 characters by Mr Watson\ is believed by him to possess leaf- 

 cushions like those of L. ohovatum ; if this is so, it is interesting, 

 as he points out, to find two distinct anatomical types associated 

 with one species. Watson thinks it probable that the " species " 

 L. ohovatum includes at least two widely different species. This 

 merely emphasizes the importance of correlating structure and 

 external characters as far as available data permit. 



X C 



Pig. 176. Lepidodendron aculeatum. 

 (Cambridge Botany School.) 



The specimen, of which part of the surface is shown in 

 fig. 174, is in all probability L. aculeatum Sternb. This was 

 described by me in detail in The Annals of Botany (1906) as 

 another example of the co-existence of the Lepidodendron fuli- 

 ginosum type of anatomy with a true Lepidodendron. The 

 locality of the specimen is not known. The leaf-cushions 

 are l'5cm. long with tapered upper and lower ends; a ligular 

 cavity may be recognised on some parts of the fossil, also faint 

 indications of leaf-trace scars. The tubercles (fig. 174, A — C, t) 

 probably represent leaf- traces which the shrinkage of the super- 

 ficial tissues has rendered visible in the lower part of their 

 course. The circular scar, s (fig. B), on the partially decorticated 

 surface is apparently a wound. The stele is sufficiently 



1 Watson (07) p. 18. 



