XXXIIl] DADOXYLON 249 



distinctive features of the primary xylem. Additional examples 

 might be quoted pointing to the tendency of recent and more 

 thorough investigation to estabhsh the fact that the occurrence 

 of Permo-Carboniferous wood of the Araucarian type does not 

 necessarily denote the existence of Cordaites. The question of 

 nomenclature is necessarily raised in this connexion. 



In recent years it has been customary to assign Palaeozoic 

 wood with Araucarian pitting to the genus Dadoxylon, while 

 wood of the same general type from more recent strata is by 

 many authors referred to Araucarioxylon} . This arbitrary dis- 

 tinction based on a difEerence in age is open to serious objection. 

 Fossil wood of the Araucarian type is widely scattered in strata 

 ranging from Carboniferous to Jurassic periods ; it also occurs 

 in later formations. The fact that on the one hand Araucarian 

 plants, as recognised by cones and fohage-shoots, are especially 

 characteristic of Jurassic floras and occur more rarely in Rhaetic 

 and Triassic floras, and on the other hand that Cordaites and its 

 alhes reached their greatest development in Permo-Carboniferous 

 times, renders it probable that in the majority of cases a distinc- 

 tive name based on geological age would be in accordance with 

 botanical differences. But we have no satisfactory data as to 

 the upper limits of the Cordaiteae or the lower hmits of the 

 Araucarineae : in all probabihty the two f amihes overlapped and 

 co-existed for more than one geological period. It is, moreover, 

 the plants from formations where overlapping occurred that are 

 the most critical from a botanical standpoint. The age-distinction 

 is therefore at best an artificial one and may be seriously mis- 

 leading. Potonie^ and Gothan^ have emphasised the desirability 

 of adopting the name Dadoxylon for all wood of the Araucarian type 

 irrespective of age. If a particular specimen can be correlated 

 definitely with Cordaites or some other genus it should be so 

 designated, but the fragmentary nature of the records usually 

 precludes this simple course. The most logical plan is to use the 

 name Dadoxylon for all woods with Araucarian characters if there 

 is no sufficient reason for employing a less provisional term. If 



i FeHx (86) A. p. 56; Knowlton (90); ZeiUer (95) B. p. 627; PenhaUow (00) 

 p. 54. 



2 Potoni^ (02) p. 229. » Gothan (05) p. 13. 



