No. 448.] NORTH AMERICAN CONIFERALES. 267 



For taxonomic purposes, the bordered pits possess a definite 

 though often hmited value. In the genus Cordaites, as also in 

 Araucarioxylon, Araucaria and Agathis, this is expressed in the 

 he.xagonal form together with their very compact, chiefly 

 multiseriate arrangement throughout the entire extent of the 

 tracheids, — characters which are of generic value and at once 

 serve to separate these genera from all others. The contrasting 

 differential feature is then to be found in the pits of the oval or 

 round form, together with their 2 -seriate or i -seriate dispo- 

 sition with a more or less marked tendency to segregation. 

 This is characteristic of the Ginkgoales and all the Coniferales, 

 both fossil and recent. 



As a different character of sub-generic value, the occurrence 

 of bordered pits on the tangential walls of the summer wood 

 of the first section of Pines — the soft pines — and their invari- 

 able absence from the same structural region in the second 

 section — the hard pines,— is one which may be always relied 

 upon. 



For the purposes of specific differentiations, the pits on the 

 tangential walls possess a distinctly inferior value which must be 

 confirmed in most cases by the evidence of other factors. 1 heir 

 utility in this respect is made sufficiently clear in the various 

 diagnoses and in the artificial key, without further discussion at 

 this time.i 



In the genus Cordaites, according to the provisional spcci c 

 differentiations of fossil forms as at present generally ^■"M>1';> • 

 the number of rows of pits, or their segn 

 groups, are characters of well de 

 are among the few features which 

 tainty for this purpose. Thus C. acadim 

 rows ; C. materiarium with 2-4 rarely 3-4 rov 

 with two rows and C. neivberryi with two 

 i which is not only ' 

 but which may be applied with full i 



