334 



THE ANATOMY OF WOODY PLANTS 



relationship of the Abietineae rather than the Araucariineae with 

 the Paleozoic gymnosperms known as Cordaitales. 



Not only do the Abietineae as a result of their anatomical 

 organization and paleobotanical history present a strong claim 

 to direct relationship with the older gymnosperms, but they 

 supply equally compelling evidence that they are ancestral to 

 other prominent coniferous subtribes. It will be well in this 



connection to 

 begin with the in- 

 ternal situation in 

 the abietineous 

 subtribe. It is 

 readily subdivided 

 into two series on 

 the basis of ana- 

 tomical structure 

 the Pineae and the 

 Abieteae. The 

 former are char- 

 acterized by the 

 possession of well- 

 developed resin 



canals in the wood 

 j n both vertical 



and horizontal 

 planes. In contrast to these, in the second series the h'gneous resin 

 canals of the secondary wood are notably absent. It is only in 

 regions recognized as conservative that they make their appear- 

 ance in the primary structures of the xylem of the root (Fig. 242), 

 in the secondary wood of the axis of the ovuliferous cone, and some- 

 times in the first annual ring of the vegetative branches. Further, 

 resin canals are found in the wood of the Abieteae as a result of in- 

 jury. Both comparative anatomical and experimental evidence, 

 as a consequence, vouch for the derivation of the Abieteae from 

 ancestral forms possessing well-developed ligneous resin canals. It 

 is of significance to note in this connection that the genus Cedrus, 

 for the great antiquity of which the geological record supplies clear 



FIG. 242. Transverse section of the root of Abies 

 balsamea, showing the presence of a resin canal in the 



