62 ROYAL SOCIETY OF CANADA 



short-cylindrical and very often have pitted walls (Fig. 24a). They 

 commonly contain resin and become more elongated the further they 

 are removed from the canal, until they finally pass into much elongated 

 wood parenchyma cells, the terminal walls of which bear bordered pits. 



The genus Abies naturally belongs to that group of conifers dis- 

 tinguished by the absence of resm passages and fusiform rays. This 

 is conspicuously true of A. balsamea, A. fraseri, A. lasiocarpa, A. mag- 

 nifica, A. amabilis, A. concolor, and A. grandis, but in A. nobilis and 

 A. bracteata we meet with important exceptions to this rule, in that 

 they show resin passages in the transverse section. In A. nobilis (Fig. 

 28), these structures lie chiefly in the central region of the summer 

 wood where they form a continuous row. In A. bracteata (Fig. 26), 

 they more commonly lie on the outer face of the summer wood as in 

 Sequoia sempervirens and in both species the structural similarity to 

 Sequoia is very marked. A longitudinal section through a resin pas- 

 sage shows again that the general relations between the epithelium 

 cells and those of the wood parenchyma are the same as in Sequoia, 

 but ,a notable difference between the two genera appears in the fact 

 that the passages of Abies are, on the whole, more perfectly organized 

 (Fig. 27). The relations between resin cells and the accompanying 

 wood parenchyma with bordered pits is further emphasized in Abies 

 amabilis (Fig. 29cd, h), where resin cells with simple pits are found 

 to lie in series coterminous with the wood parenchyma having bor- 

 dered pits. Abies also affords somewhat conclusive evidence as to the 

 relations between resin cells and resin passages. In all the first named 

 species where no resin passages occur, resin cells are well defined; 

 but in A. bracteata and A. nobilis, they are found with considerable 

 difficulty, seeming to suggest that they have been replaced by the 

 former. This replacement becomes more clearly understood in the 

 light of the facts already presented, which go to show that the resin 

 passage is, after all, only a final expression of certain conditions of 

 aggregation in the resin cells, whereby the formation of resin becomes 

 more centralized. 



Our studies of the resin passages go to show that while Sequoia 

 gigantea, Juniperus communis, Libocedrus decurrens and Cupressus 

 gaudaloupensis manifest a definite tendency toward the formation of 

 resin passages, these structures are never fully organized. In Sequoia 

 sempervirens, on the other hand, such resin passages are imperfectly 

 developed, though they are never associated with radial canals such 

 as occur in Picea or Larix. As this species is now known to extend 

 far back into Cretaceous time, it is evident that this character is one 

 which has survived for a great length of time, and may therefore be 

 regarded as truly fixed and characteristic of the species. 



