3o8 MORPHOLOGY OF GYMNOSPERMS 



their number. It is very probable, according to Jeffrey, that 

 Yezonia is the same as Brachyphyllum, the commonest conifer 

 (araucarian) of the later Mesozoic in the Atlantic coastal region of 

 the United States. Whatever the peculiar anatomy of the leaves of 

 Yezonia may suggest as to relationships, the structure of the seed, 

 with its completely free nucellus, suggests either a remarkably per- 

 sistent retention of an ancient character, or an abandormient of the 

 idea that such a character is necessarily ancient. Moreover, in these 

 detached seeds no embryos were found, adding force to the suggestion, 

 made in connection with paleozoic seeds, that the absence of embryos 

 is not a paleozoic character, but a character of seeds prematurely 

 detached. 



7. Interrelationship of the tribes 



All the evidence of morphology, vascular anatomy, and history 

 favors the belief that the Taxodineae and Cupressineae have been 

 derived from the much more primitive stock of the Abietineae; and 

 these two branches may be assumed to have arisen during the 

 Mesozoic. 



The discussion of relationship, however, has really to do with the 

 Abietineae and Araucarineae, and to this discussion history can 

 contribute nothing decisive. The apparent anatomical connection 

 of these two tribes, suggesting genetic relationship, has been men- 

 tioned, and Jeffrey has concluded that the Araucarineae have been 

 derived from the primitive stock of the Abietineae. The general 

 outline of the argument is as follows. That abietineous wood with 

 resin canals only as a result of injury (as in Cedrus, Abies, Tsuga, 

 Pseudolarix) is less ancient than that in which resin canals are a 

 normal feature (as in Pinus), is shown by the greater geological age 

 of the latter; and this is indicated further by such a Pinus-liks form 

 as Prepinus, which, in addition to its resin canals, has foliar vascular 

 bundles identical with those of Cordaitales. The inference is that 

 a resin canal produced by wounding is a "reversionary character." 

 These wound reactions occur in both of the fossil araucarian types 

 of wood known as Brachyoxylon and Araucariopitys, but not in living 

 araucarians; and since these two types show also a combination of 

 araucarian and abietineous pitting, both in the secondary wood and 



