ANATOMY AND I'll V LOGENY OF THE CONIFERALES. 



447 



of the formation of traumatic resin canals in the wood of both the root and the stem of 

 S. gigantea and consequently ana of the opinion that it is quite a usual result of injury. 

 It should be added, however, that the formation of parenchymatous wood containing a 

 Large number of resin cells and ordinary parenchyma cells is even more commonly 

 present in the case of wounds. This is especially the case with large exposed wounds on 

 the aerial portions of the stem, where there is much necrosis and drying out of the woody 

 tissue. In smaller wounds, however, where there is not too great an exposure of the 

 ligneous cylinder to desiccation, the formation of the traumatic resin passages described 

 above is very common. It should be noted finally that the traumatic resin canals of S. 

 gigantea are formed in the vernal wood and in this respect are in contrast to those occur- 

 ring in S. semper vsir ens under similar conditions, which, as will be shown later, make their 

 appearance in the autumnal wood. 1 have found examples of the formation of resin 

 canals in the phloem of 8. gigantea, as well as in the wood, and as the result of a similar 

 cause. I have discovered no instance of the occurrence of resin ducts in the fibrovascular 

 cylinder of this species, except in the first year's growth of vigorous young branches of 

 adult trees and in the axis of female cones (as described in earlier paragraphs) , which 

 could not be clearly traced to a previous injury. It seems extremely probable that the 

 formation of traumatic resin canals in S. gigantea is to be regarded as a case of reversion 

 to an ancestral condition, especially in view of the mode of occurrence of normal resin 

 canals in certain instances as described above. The arguments in favor of this view, how- 

 ever, are best deferred to a later stage. 



Traumatic Resin Canals of the Abietineae. 



It seems necessary in the meantime to refer preliminarily to certain other facts of a 

 similar nature which have been made out in the case of the Abietineae, in a series of 

 researches of which the present investigation forms a part. It has long been known that 

 resin ducts are generally absent in the wood of the Abietineous genera, Abies, Tsuga, and 

 Cedrus, and that they are replaced in many instances by resin cells. For the present the 

 first-named genus will alone be considered ; for as I hope to show subsequently, the other 

 two genera resemble it very closely in the features which are of interest in this con- 

 nection. Abies firma is described by Prantl (Engler u. Prantl, Nat. pflanzenfamilien, 

 Coniferae, 1889, p. 37) as differing from the other species of Abies in normally possessing 

 resin ducts in its wood. Penhallow (op. cit.) has more recently described the presence 

 of resin canals, occurring in isolated annual rings of Abies nobilis and Abies bracteata. 

 I have been able to confirm these observations in the beautiful series of sections of North 

 American woods published a few years ago by Professor Penhallow. The resin ducts 



