130 



CONIFERALES (RECENT) 



[CH. 





great majority of Conifers which are normally without resin-canals 

 in the wood have the power of producing them in response to 

 traumatic stimuli. In Cedrus, Pseudolarix, and Tsuga resin- 

 canals are usually confined to the primary xylem of the root but 

 wounding induces the development of canals in other parts of the 

 wood. In Cedrus, however, both horizontal and vertical trau- 

 matic canals may occur whereas in other Abietineae the traumatic 

 canals are only vertical 1 . Kesin-canals may occur in the first-year 

 wood of some species of Abies (fig. 690, B) and in Sequoia gigantea 

 they are present in the first-year wood of vigorous branches and 

 in the peduncles of cones, but do not normally occur in the later 

 wood. In S. sempervirens canals are as a rule absent and are 

 developed only after wounding (fig. 690, A). In the Araucarineae 



A B 



FIG. 690. A, Sequoia sempervirens. B, Abies sp. showing traumatic canals in the 

 wood. (After Jeffrey.) 



resin-canals are absent nor are they produced in injured stems : 

 this failure to produce canals in response to disturbances set up 

 by wounds is considered by Jeffrey to be an indication of the 

 relatively late evolution of the family. Pinus, with abundant 

 canals, is regarded as one of the more primitive types; Abies, 

 with very few canals in healthy specimens but readily producing 

 them on wounding (fig. 690, B), is regarded as a slightly later 

 product of evolution, while Sequoia sempervirens (fig. 690, A) in 

 which traumatic canals alone occur is still further removed from 

 the original stock, and the Araucarineae, which are considered to 



1 Jeffrey (05) p. 25. 



II 



