568 PROCEEDIXGS OF THE AMERICAN ACADEMY. 



of evidence in favor of the derivation of the Araucarian tribe from 

 Abietineous ancestors. 



Having in the present article and those which have preceded it, 

 considered a number of anatomical features presented by the Arau- 

 carioxylon type and by the living genera Avith the same type of wood, 

 we are in a position to discuss its affinities and evolutionary develop- 

 ment. It has l)een pointed out in the first article that there is the 

 best of evidence, derived from both fossil and living forms, that woods 

 of the Araucarioxylon type were originally characterized by the pos- 

 session of strongly pitted ra\'s and abundant wood parenchA'ma. 

 These features are quite inconsistent with a direct connection of this 

 type with the Cordaitean plexus of g^'mnosperms, since here, we know, 

 •that the wood was entirely without wood parenchyma and the rays 

 were composed of cells with unpitted walls. Passing to the next 

 important item of wood structure, we find that there is every reason 

 to believe that the older Araucarian conifers were not characterized 

 * by alternating or compressed pitting. On the contrary the radial 

 pits were often opposite and moreover were separated from one another, 

 particularly towards the ends of the tracheids, by cellulose bars im- 

 bedded transversely in the lignified wall of the tracheids. Bars of 

 this type do not occur in any Cordaitean woods but are found in the 

 mature wood of all existing Conifers, except the livhig Araucariineae. 

 It follows that on the basis of pitting and the cellulose bars of Sanio, 

 the Araucarian conifers were derived from the same ancestors as the 

 remaining coniferous tribes. It is further clear both from a considera- 

 tion of comparatiA'e anatomy and from the organization of the older 

 woods belonging to the Araucariineae, that the absence of resin canals 

 is not a primitiAc feature of Araucarian woods, since the progenitors 

 of the stock clearly possessed them. The present article appears 

 moreover to make it clear that persistent leaf traces are not an an- 

 cestral feature of organization of the Araucarian stock, both the 

 anatomical conditions found in the older forms and in the seedlings 

 of the li\ing genera, showing beyond any reasonable doubt, on gen- 

 erally accepted biological principles, that the leaf strand in the ances- 

 tors of the Araucarian stock, persisted only for a few years, as is 

 characteristically the case in all other living conifers. 



It is apposite to consider if other facts justify the conclusion reached 

 in connection with the present investigation, namely that the Arau- 

 carian stock is distinctly coniferous and is neither the most ancient 

 tribe of the Coniferales, nor connects them with those ancient Gymno- 

 sperms, which the majority of competent morphologists regard as 



