CONIFERALES (PINACEAE) 309 



in the medullary rays (p. 306), the mo\emenl of evolution seems to have 

 been from the Abietineae toward the Araucarineae. It would fol- 

 low that the modern araucarians have come from ancestors (like 

 Ara near io pity s) allied to the x\bietineae through such intermediate 

 forms as Brachyphyllum and its allies (with Brachyoxylon wood). 

 It is evident that these cretaceous types could not have made the actual 

 connection with Abietineae, but they may represent the structure of 

 much more ancient forms that did. 



One objection to the abietineous origin of araucarians is that the 

 latter were a dominant type during the Mesozoic, while the Abietineae 

 seem to have been scantily represented. At present it is an assump- 

 tion that the Abietineae were poorly represented, and so far as there 

 is any proof to the contrary, Piniis may have been represented by 

 as many species during the Cretaceous as now. At the same time it 

 must be remembered that these resemblances and the historical record 

 would be satisfied by the independent origin of the two tribes from 

 such a common ancestry as the Cordaitales. Therefore, so far as 

 the present evidence goes, it is satisfied with two alternatives: either 

 the Araucarineae were derived from the Abietineae at a very early 

 period, or the two tribes arose independently and about the same time 

 from the same ancestral stock. 



8. Relationship to other gymnosperms 



The question of the origin of the Pinaceae was involved in the 

 discussion of the interrelationship of the tribes. There seems no 

 reason to doubt that the primitive stock came from the Cordaitales, 

 either an abietineous stock alone, which gave rise to the other tribes, 

 or such a- stock accompanied by a separate araucarian phylum. It 

 must be remembered that Cordaitales include a range of forms 

 much more extensive than the Cordaitineae (Cordaiteae), forms 

 which show intergrading characters between Cordaitineae and Cycado- 

 filicales. It is from such a plexus that Coniferales as a whole may be 

 claimed to have been derived. To present the data which favor this 

 connection with the Cordaitales would be to rehearse the facts of 

 structure and of history that have been presented in connection with 

 the two groups. With Cycadofilicales and Cordaitales in mind as the 

 dominant paleozoic groups of gymnosperms, the latter as clearly 



