352 THE ANATOMY OF WOODY PLANTS 



of Pinus and Prepinus resembles that of Ginkgo in possessing 

 opposite pitting and bars of Sanio, this organization contrasting 

 with the tracheary structure of older types like the Cordaitales 

 and the Cycadales in reality presents no difficulty. For in prim- 

 itive regions and organs the alternating pitting without bars of 

 Sanio characteristic of the Cordaitales is present in the Abietineae 

 (particularly in Pinus and Prepinus}, and passes by gradual 

 transitions into the opposite pitting with bars of Sanio exemplified 

 in the structure of the mature wood both in Ginkgo and in the 

 Abietineae. The reproductive structures of the Cordaitales are 

 too little known to us to supply appropriate points of comparison. 

 It may be stated in summary that the Abietineae present as good 

 anatomical evidence for derivation from the Cordaitales as do 

 the Ginkgoales; and, moreover, they have an additional claim to 

 such affinity by their clear relationship with the Ginkgoales. 



But it is not only by reason of resemblances to the Ginkgoales 

 and the Cordaitales, neither few nor unimportant, that the Abie- 

 tineae show themselves to be a primitive subtribe of the Coniferales. 

 When the anatomical organization of the remaining coniferous 

 subtribes is investigated in the light of the general principles so 

 often emphasized in the present volume, it supplies in many cases 

 distinct evidence that the Abietineae are the primitive stock from 

 which all have taken their origin. This situation may be illus- 

 trated first in the case of the Araucariineae, which are somewhat 

 generally regarded as the primitive conifers and those most nearly 

 connected with the Cordaitales. The strongest evidence for this 

 claim is supplied by the organization of the tracheids, presenting 

 the same alternating pitting and the absence of bars of Sanio as 

 are manifested in the cordaitean and cycadalian gymnosperms. 

 If alternating pitting alone were a sufficient criterion of relation- 

 ship, many angiosperms by the possession of this feature could 

 establish a claim to relationship with that ancient group of gymno- 

 sperms. The evidence here as in other cases should be read in 

 the light of the general principles of comparative anatomy. The 

 longitudinal radial section of the cone axis, and to a lesser extent 

 of the leaf trace, of either Araucaria or Agathis at once reveals 

 the true situation. In these cases one always finds bars of Sanio 



