6 EDWARD C. JEFFREY ON 



('84) has pointed out, Picea in contrast to the other Ahietineous genera, has the resin 

 canals of the leaves at first continuous with those of the stem, but the free communication 

 between the two systems is cut off at an early date by the formation of absciss periderm. 

 This continuity between the foliar and the axial systems of resin canals appears to have 

 been the primitive condition for the Abietineae, but as has been indicated above, has 

 become obsolete in most of the existing species. 



Figure 8, plate 1, shows the effect of injury on the structure of the wood in Picea 

 nigra. The sparse and small resin canals present in the normal wood are replaced by 

 close tangential rows of resin ducts of much larger lumen, in the folds of traumatic wood, 

 which in the course of time grow over the injured surface of the stem. The reaction 

 which leads to the formation of the tangential rows of canals in the case of injury, is of 

 course much more intense in the immediate vicinity of the wound, and fades away tan- 

 gentially in the newly formed wood. The traumatic resin canals in question communi- 

 cate tangentially and have doubtless the function of pouring out resin over the wounded 

 portion of the stem. It is an interesting fact, that the formation of these tangential rows 

 of traumatic resin canals in the Abietineae is most marked in those genera in which the 

 resin canals are normally somewhat sparse or entirely absent. In Pinus, where the resin 

 ducts of the wood are abundant in both the vertical and the horizontal planes, a marked 

 reaction leading to the formation of tangential rows of traumatic resin ducts seldom or 

 never occurs. Iu Picea, Larix, and Pseudotsuga, on the other hand, their formation is an 

 almost invariable sequel to injury, and this is even more strikingly the case in Abies, 

 Tsuga, Cedrus, and Pseudolarix, which are ordinarily described as entirely lacking ligne- 

 ous resin ducts. In the genus at present under discussion, I have noticed a strong forma- 

 tion of traumatic resin canals, not only as the result of mechanical injury, but also as 

 a sequel of the attacks of Chermes abietis, and of parasitic rust fungi producing witches' 

 brooms. 



In Picea the leaf trace is described by Bertrand ('74) as being a double one by the 

 presence of a distinct median medullary ray. In P. nigra the foliar trace leaves the 

 central cylinder of the axis as a single strand of very small size. As it reaches prox- 

 imity to the base of the leaf it becomes distinctly double, as may be seen in figure 9, 

 plate 2. In P. engelmanni, which was also examined in this connection, the trace is 

 somewhat larger and the duplication correspondingly more marked. The root in Picea 

 does not differ in any marked features from those of Larix and Pseudotsuga. 



Abies. 



In Abies balsamea Mill., resin canals are normally quite absent in the wood of the 

 shoot. This feature is illustrated by the central portion of figure 10, plate 1. In 



