JEFFREY. — ARAUCARIOXYLON TYPE. 549 



Summary. 



1. The characteristic pitting of the wood in Agathis anfl Aran- 

 caria, the Araucarioxylon type, is not ancestral hut more recently 

 acquired. 



2. This conclusion is based on the structure of the first annual ring 

 of the stem in iVIesozoic Araucarioxyla. It is confirmed strongly 

 by the seedling structure of the living genera and particularly by the 

 anatomical structure of the wood of their cone axes. 



3. The cellulose bars of Sanio, characteristic of the mature wood of 

 all living genera of the Coniferales, except Agathis and Araucaria, are 

 clearly present in the secondary tracheids adjacent to the primary 

 wood of the cone axis in these two genera. They are absent in the 

 seedling and cannot be clearly discerned in the leaf traces on account 

 of the small size of the elements. 



4. Since bars of Sanio do not occur in similar situations in Cycas 

 and Ginkgo, it cannot be assumed that they are a feature of all gymno- 

 spermous woods in proximity to the primary xylem. 



5. Since deviations of a significant nature in the pitting and struc- 

 ture of the tracheids occur in primitive regions of the Araucarian axes, 

 which connect them with the remaining tribes of the Coniferales stock, 

 it follows that so far as these features are concerned, the Araucarian 

 Conifers are derived from the common coniferous plexus and are not 

 directly articulated with the Cordaitales. 



6. On the basis of comparative studies of the tracheids of the 

 Araucariineae, they cannot be regarded as primitive representatives 

 of the Coniferous order. 



7. The real affinities of the Araucariineae can best be defined when 

 all the evidence is considered in the concluding article of this series. 



