No. 448.] NORTH AMERICAN CONIFERALES. 



Such : 



brings i 



ng relief the fact that tht 



Araucarias, both past and present, 

 group with a somewhat wide range of variations, and in this 

 respect they may be said to stand between the more stable Cord- 

 aites and Agathis on the one hand, and the far more variable 

 Coniferje on the other, since in Agathis anstralis we find essenti- 



ally the : 



features of : 



distributK 



Cord- 







0© 















® 











® 



aites, the pits being 1-3-seriate. The sequence presentee ao()\c 

 may be held to be in the inverse order of dcNeloi^ment, and A. 

 robcrtiaiinm must therefore be held to represent the most primi- 

 tive form. 



It is apparent that in Cordaites, Araucaria (including Arauai- 

 rioxylon) and Agathis, the pits are invariably distinguished n 

 two constant features; (i) their hexagonal form and (2) Ihcir 

 very compact disposition throughout the entire extent of the 

 tracheid. They often deviate from the multiseriate arrangement 

 typical of the group as a whole, in that in individual cases the)- 

 are reduced to a i-seriate arrangement. They thus tend to 

 overlap the next group which is distinguished by a 2-senate dis- 

 position, but any confusion which might arise from this cause, 

 may be overcome by reference to the special form and dis- 



