74 



THE ANATOMY OF WOODY PLANTS 



reversion. This general doctrine will receive particular considera- 

 tion at a later stage and consequently need not be elucidated here. 

 If the radial tracheids occurring under the conditions described in 

 the foregoing paragraph are interpreted as a reversion to an ances- 

 tral condition, it follows that the simple type of ray found in Abies 

 and in the Cupressineae or Taxodineae is by no means primitive, 



but is the result of 

 simplification from 

 the more complex 

 state of organiza- 

 tion of the ray, 

 characteristic of 

 the lower living 

 Abietineae. Obvi- 

 ously an experi- 

 mental as well as a 

 purely anatomical 

 investigation of 

 ray structures is 

 necessary for their 

 complete morpho- 

 logical and evolu- 

 tionary under- 

 standing. 



Not only does 



one find in the case of certain coniferous woods of simpler 

 organization evidence of derivation from ancestral types present- 

 ing the complication of marginal ray-tracheids, but likewise in the 

 genus Cedrus among the Abieteae, which has normally only 

 linear or uniseriate rays, fusiform radial structures containing 

 horizontal resin canals are found. This situation is made clear 

 by Figs. 54 and 55, which present tangential views of the normal 

 and injured wood of Cedrus Libani (the cedar of Lebanon). In the 

 traumatic or injured wood of cedar, which, so far as the geological 

 record supplies us with definite evidence, is the oldest representative 

 of the Abieteae or firlike conifers, we have clearly indicated a 

 condition ensuing from injury which definitely unites the cedar 



FIG. 54. Tangential section of the normal wood of 

 Cedrus Libani. 



