CONTRIBUTIONS FROM THE PHANEROGAMIC LABORATORIES 

 OF HARVARD UNIVERSITY. NO. 55. 



THE HISTORY, COMPARATIVE ANATOMY AND EVOLU- 

 TION OF THE ARAUCARIOXYLON TYPE. 



By Edward C. Jeffrey. 



Received, September 28, 1912. 



Part I. 



Fossil woods of the Araucarioxylon type are extremely abundant 

 in the Mesozoic deposits. The only living conifers with wood of 

 this type are confined to the Eastern tropical region, to Australasia 

 and to South America and are all included under the two genera 

 Agathis and Araucaria. As a consequence of their habit, which 

 differs from that of all living Conifers, except certain of the Podo- 

 carpineae, and of the organization of their woody tissues, the Arau- 

 carian Conifers haxe been most commonly referred to affinities with 

 the Cordaitales, an important gymnospermous group of the Paleozoic. 

 As will be shown in connection with the present investigations, the 

 importance of these features of resemblance has apparently been much 

 exaggerated. The association with the Cordaitales carries with it 

 th-e implication, that the Araucariineae are either the ancestors of 

 the other existing coniferous tribes, as is quite commonly held, or else 

 that they constitute a separate line of descent, distinct from the 

 ancestral stock of the remaining Conifers, as has been maintained in 

 recent years by Seward and Penhallow. It is obviously a matter of 

 considerable importance to clear up the affinities of the Araucarian 

 stock, not only from the standpoint of its particular origin; but on 

 account of the light thus to l)e thrown on the vexed subject of evolu- 

 tionary processes as a whole by reason of the abundant display of the 

 group during so long a period of geological time. The present writer 

 has devoted nearly ten years to the procuring of material of Araucarian 

 Conifers living and extinct and to the developmental, experimental 

 and comparative anatomical investigation of their various organs and 

 tissues. 



