26 PENHALLOW ON 



An examinatiou of the internal structure shows that the foUowiug characters are 

 common to all the sections. The structure is coarsely cellular. In transverse section 

 the cells are variable in size, averaging about 50 /< in diameter. The walls are not 

 well defined and continuous, but are often poorly defined and consist of a granulated 

 carbonaceous substance which often becomes irregularly scattered, sometimes intruding 

 upon the cell cavity, though in most cases localized along definite lines. We have found 

 cells of only one kind, and are therefore unable to confirm the statement of the original 

 description to the effect that "the appearance of rings of growth is caused by large cells 

 disposed in concentric, narrow bands between the wider bands of fine, fibrous tissue," 

 although from analogy we should infer that this might have been the case in the original 

 stem. 



In longitudinal section the cells are found to present the same appearance as to their 

 general characteristics, as in the transverse section, and also a marked similarity in size — 

 measuring about 50 /' in diameter. There is, however, a more or less marked tendency, as 

 noted in the original description, for the cells to fall into longitudinal rows which follow 

 a somewhat vermicular course. This is most conspicuous under a low power, although 

 to be observed, in many cases, under a ^ objective. 



My measurements show that, as determined from cells taken at random, the average 

 size in transverse section is 48 /^ the range being from 40 /' to 70 /'. In longitudinal 

 section, the same number of measurements give an average of 54 //, and. an extreme range 

 between 30 /< and 70 //. 



These facts, taken in connection with the similarity here noted between this plant and 

 Nematophyton in certain conditions, lead to the conclusion that it is only a highly altered 

 condition of this latter. This view is also supported by the opinion expressed some time 

 since, by Sir Wm. Dawson that " Celluloxlon is allied to Prototaxites." ' 



Fu.rthermore, while it is quite possible that this may have been a distinct species, 

 which I have no present means of proving, the fact that it occurs in the Middle Brian 

 and not in the lower horizon, where alone N. Logani has been found, together with the 

 probability that the radial openings of N. Logatii were represented here by scattered, open 

 areas of small size as in N. crassum, would lead one to refer it, for the iiresent at least, to 

 the latter species. 



Nematoxylon tenue, Dn. 



This ijlaut was originally described by Sir Wm. Dawson, as follows - : — 



"Slender stems with thick, coaly bark and woody fibres of much smaller diameter 



than in the last species (iV. crassum) and marked with minute dots." In connection with 



this it was also stated that " the stems of this sjiecies are small, not exceeding half an inch 



in diameter, but are distinctly surrounded by a thick, shining, coaly bark. The wood is 



calcified and appears to be perfectly homogeneous It may l)e doubted if this 



species has any real affinity with the last (N. crassum), but they correspond in their 

 negative characters, and both appear to indicate the existence of certain woody plants of 

 singularly simj)le and homogeneous structiire." 



' Geolog. Surv. of Canada, Fossil Plants, part ii, p. 126. 

 2 Quart. Jn'l. Geol. Soc, Nov. 1863, 467. 



