3i8 THE ANATOMY OF WOODY PLANTS 



is nothing in common between the anatomical structures of vege- 

 tative and reproductive parts in Ginkgo and the Taxineae. A 

 later, but apparently equally erroneous, tendency is to interpret 

 the evolutionary sequence of the Coniferales entirely in the light 

 of the data derived from the study of Paleozoic gymnosperms. 

 This attitude is of course found strongly in evidence in those 

 countries which have contributed notably to the elucidation of 

 the organization of the seed plants of the Paleozoic. By those 

 who are affected by the Paleozoic bias the araucarian subtribe of 

 the Coniferales is considered the oldest representative of the 

 group. There are those again who attempt to reconcile the 

 taxinean and araucarian hypotheses of derivation by the assump- 

 tion that the Araucariineae have come from the Cordaitales, 

 while the remaining coniferous subtribes have been derived from 

 the Taxineae. The hypothesis of a lycopodineous origin of the 

 group has been put forward at various times, but need only be 

 mentioned here, as it has few advocates and does not appear to 

 derive any support from paleobotanical or anatomical facts. 

 The views in regard to the phylogeny and evolution of the Co- 

 niferales adopted in the present work represent an attempt to 

 interpret this large and important group of gymnosperms in the 

 light supplied by the anatomy of Mesozoic forms as compared 

 with representatives of the group still living. The method of 

 treatment adopted will be, so far as the limits of space in an ele- 

 mentary textbook permit, purely inductive. As has been em- 

 phasized in an earlier paragraph, the conifers, on account of their 

 abundant presence in the floras past and present, supply a most 

 valuable document for the interpretation of the fundamental 

 principles of evolution. 



Since the araucarian conifers are quite generally regarded 

 at the present time as the primitive representatives of the group, 

 it will serve a useful purpose to consider these first. A transverse 

 section of the wood of the stem in this subtribe (Fig. 225) generally 

 reveals the presence of annual rings, unless the particular species 

 under investigation happens to be of lowland tropical origin. The 

 autumnal tracheids are marked by tangential pitting, a general 

 feature of organization of the more modern gymnosperms. The 



