CHAPTER X 



RESIN PASSAGES (continued) 

 DISTRIBUTION AND PHYLOGENY 



Prantl (62, 37) states that resin passages occur in the wood 

 of "most Abietineae, namely, Pseudotsuga, Picea, Larix, Pinus, 

 and Abies firma." This statement requires some modification 

 in detail, especially with respect to the last-named genus, and 

 in order to make the results of the present studies clear it will 

 be expedient to discuss separately the distribution of the resin 

 cysts and the resin passages. 



The first species to which our attention may be directed is 

 Tsuga Mertensiana. This is the only species of the genus in 

 which definite resin cysts are to be found. Such structures are 

 never numerous, and they take the form of short rows of con- 

 tiguous cysts in the initial layer of the summer wood of distant 

 growth rings. Longitudinally they have no definite limits, but 

 they appear to be extended for great distances, and probably 

 through the entire longitudinal growth of the season, at least. 

 There is no obvious alteration either in the position or volume 

 of the resinous contents of the isolated resin cells which lie on 

 the outer face of the summer wood. The constancy with which 

 these structures occur gives to them a definite value for the 

 recognition of the species, and permits us to differentiate it 

 from T. caroliniana on the one hand, and from the remaining 

 three species on the other. 



In the genus Abies only four species out of eleven show 

 resin cysts. These are A. bracteata, A. nobilis, A. concolor, 

 and A. firma. Referring again to Prantl's observation (62, 37), 

 it must be pointed out that his statement with respect to the 

 occurrence of resin passages in A. firma requires modification in 



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