CONTRIBUTIONS FROM THE PHANEROGAMIC LABORATORIES 

 OF HARVARD UNIVERSITY. NO. 56. 



THE HISTORY, COMPARATIVE ANATOMY AND EVOLU- 

 TION OF THE ARAUCARIOXYLON TYPE. 



By Edward C. Jeffrey. 



Part II. 



In the first article of the present series the structure of the rays and 

 the parenchyma of woods of Araucarian affinities, was considered. 

 In the present one the characteristic features of the tracheids and the 

 nature of the pitting will be particularly discussed. The pitting of the 

 tracheary elements in the Araucarian Conifers has been considered 

 by practically all writers as an infallible criterion for the diagnosis 

 of their woods as fossils. It is unnecessary to enter upon this matter 

 in detail as the literature on the subject has quite recently been 

 admirably summarized by Gothan.^^ It is universally assumed that 

 crowded radial pits on the tracheid walls either flattened by mutual 

 contact, if the pores are uniseriate, or of somewhat polygonal outline 

 in case the pits are in several rows, indicate Araucarian affinities. 

 Recently however a tendency to question the universal validity of the 

 Araucarian type of tracheary pitting as an indication of Araucarian 

 affinities has made itself felt. On the one hand it has been maintained 

 that woods with typical Araucarian pitting in reality were referable 

 to the Abietineae on the assumed more important character of their 

 ray structure. ^^ On the other it has been maintained that woods with- 

 out typical Araucarian pitting in reality belonged, in consideration 

 of the sum of their characters to the Araucarian Conifers. ^^ The 



15 Zur Anatomie lobendcr u. fossilcr Gymnospcrnien-Holzer, Berlin (1905). 



16 Gothan, Die Fossilen Holzer von Konig Karl's Land, Kung. Svensk. 

 Handlingar, Bd. 42, and Gothan, Die Fossilen Hoelzreste von Spitzbergen, 

 Kung. Svensk. Vetenskap Handlingar, Bd. 45. 



17 Gerry, Eloise, Distribution of the bars of Sanio in the Conifers. Ann. 

 Bot. 24 (iyiO); Sinnott, E. W., Paracedroxylon, a new type of Araucarian 

 wood, Rhodora, ll;JcfTrey, E. C., The Affinities of Geinitzia graciUiina, Bot. 

 Gazette, 50. 



