556 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Conifers to the Abietineae and bases his position on the structure of 

 the rays, which he claims is the most trustworthy diagnostic char- 

 acter of coniferous woods. That is a view to which the present writer 

 cannot subscribe, as from an extended comparative, anatomical, 

 developmental, experimental, and paleobotanical acquaintance with 

 coniferous woods he is in the position to state that wide variations 

 of ray structure occur within all the coniferous tribes, and that as a 

 consequence this feature of the organization of the wood cannot be 

 successfully employed for the diagnosis of the woods of extinct 

 conifers. It has been pointed out in the first article of this series, 

 that even in so highly specialized an Araucarian species as Agathis 

 australis, rays of the Abietineous type occur normally in the wood 

 of the cone and may be readily produced traumatically in the wood 

 of the root. A similar illustration may be cited in the case of 

 Sequoia. As is well known the rays in the Sequoiineae are usually 

 composed of thin walled cells without intercommunicating pits. In 

 the cones of both the living species of Sequoia, particularly S. gigantea, 

 the cells of the rays of the woody axis are very strongly pitted, espe- 

 cially towards the primary wood. Further in this genus strongly pitted 

 rays appear as the result of injury. It appears quite clear from the 

 conditions in the case of Agathis australis and Sequoia gigantea, that 

 ray structure may vary greatly within the same genus and even the 

 same species and consequently cannot be as an infallible diagnostic 

 feature. The presence of rays of the Abietineous type consequently 

 cannot be taken as satisfactory proof that the Jurassic woods under 

 discussion are in reality Abietineous. This consideration likewise 

 applies to the presence of traumatic resin canals because if these alone 

 were a sufficient diagnostic character, we would be compelled to put 

 the wounded wood and normal cone axes of Sequoia gigantea under 

 the Abietineae, although the sum of characters of that species by com- 

 mon consent justify the placing of it in an entirely distinct tribe. Let 

 us now turn to more constant characters than ray structure or trau- 

 matic resin-canals, namely the pitting of the tracheids which has 

 been admitted by all experts, with the sole exception of Dr. Gothan, 

 as an important Araucarian diagnostic feature. In the Jurassic 

 woods under discussion the radial pitting of the tracheids is distinctly 

 of the Araucarian type. Further we have recently had added to the 

 list of utilizable diagnostic characters of Araucarian woods, the absence 

 of the cellulose bars of Sanio, as worked out by Miss Gerry. ^^ True 



37 Op. cil. 



