JEFFREY. — ARAUCARIOXYLON TYPE. 545 



Before passing to the consideration of the significance of these struc- 

 tural features of the wood of the cone in Amucaria Bidwillii, it will 

 be well to examine them more particularly in this species and discover 

 their occurrence and developnicnt in other species of Araucaria as well 

 as in species of the allied genus Agathis. 



Figure a, Plate 6, illustrates the conditions presented in another 

 photograph of a radial section of the wood in Araucaria Bidwillii. 

 Here although the magnification is not great the bars of Sanio stand 

 out with great clearness between the pits, which on the whole tend 

 more in their arrangement to the typical Araucarian condition of 

 alternation than in the figures described above. The tracheitis are 

 bounded above and below by wood rays, showing that although 

 they lie near the primary wood they are typical elements of the second- 

 ary xylem. Figure b, Plate 6, shows a very highly magnified view of 

 parts of three tracheids of the secondary wood in proximity to the 

 primary xylem. Here it is possible to distinguish the bars of Sanio 

 with great clearness. They are as a rule, invariabl}^ in the figure under 

 discussion, not continuous across the tracheid, but subtend usually 

 the breadth of a single pit. The forking of the cellulose bars at the ends 

 can be clearly made out. 



Figure c, Plate 6, shows the conditions in the tracheids of the second- 

 ary wood, adjacent to the primary xylem in Araucaria imbricata, very 

 highly magnified. On one side of the figure can be seen a spirally 

 sculptured element of the primary xylem. On the other, one tracheid 

 in particular shows clear bars of Sanio. In Araucaria imbricata 

 which, as will be shown later, as a result of the consideration of a 

 number of lines of evidence is among the least primitive species of the 

 genus, the tracheids showing well spaced pits and clearly discernible 

 bars of Sanio are very few in number. Araucaria CooJcii and Arau- 

 caria Rulei were likewise examincfl, with results intermediate between 

 those found in A. Bidwillii and A. imbricata which appear in these as 

 in other respects to represent the extreme conditions found in the 

 genus. 



P^or comparison an illustration of the conditions in the mature 

 secondary wood of Pinus strobus is shown in Figure d, Plate 6. 

 Here the cellulose bars of Sanio are very distinct between the uni- or 

 bi-seriate pits. The pits where they are in two rows are opposite. 

 The occasional forking of the bars at the ends can likewise be made 

 out. The pits are well spaced and rounded. 



Figure e, Plate 6, shows a tracheid wall of Araucaria Bidwillii in 

 tangential section. That the plane of section is in reality tangential 



