CONIFERALES 



329 



anatomy, have assumed that the transitional woods in question 

 are those of Abietineae which are losing their primitive araucarian 

 characters. A fatal objection to this point of view, however, is 

 the fact that none of these transitional woods shows the presence 

 of bars of Sanio. In other words, they must clearly be diagnosed 

 as belonging to the araucarian side on the basis of the most reliable 

 of diagnostics of coniferous woods bars of Sanio. Attempts 

 in the direction of proving 

 the woods in question 

 abietineous rather than 

 araucarian have chiefly 

 taken the form of discus- 

 sions as to the value of ray 

 structure in the diagnosis 

 of coniferous woods. It is 

 beyond the range of the 

 present volume to discuss 

 details of the organization 

 of the radial structures in 

 the Coniferales; but it may 

 be stated in a general way 



FIG. 237. Wood of Brachyoxylon formed 

 after wounding. 



and on the basis of com- 

 parative anatomy that no 

 feature is more subject to variability within the limits of a single 

 subtribe and hence is less available for comprehensive conclusions 

 in regard to evolutionary sequence. A final argument against the 

 araucarian descent of the Coniferales from the Cordaitales is 

 supplied by the extremely abundant Mesozoic araucarian type 

 of wood known as Brachyoxylon. In wounded specimens of wood 

 of this genus traumatic resin canals are formed (Fig. 237), 

 resembling those of the normal wood of the pinelike conifers. 

 The occurrence of resin canals as a consequence of injury in 

 Brachyoxylon, in view of the fact that this genus is admitted 

 by competent paleobotanists to be of unquestionable araucarian 

 affinities, is of great significance. This being the case, we are 

 justified in interpreting the canals formed after wounding as a 

 reversionary phenomenon, indicating relationship to the pinelike 



