BORDERED PITS 71 



the first section of Finns (the soft pines) and their almost 

 invariable 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. Their 

 utility in this respect is made sufficiently clear in the various 

 diagnoses and in the artificial key, without further discussion 

 at this time. 



In the genus Cordaites, according to the provisional specific 

 differentiations of fossil forms as at present generally employed, 

 the number of rows of pits, or their segregation into definite 

 groups, are characters of well-defined specific value, since they 

 are among the few features which maybe utilized with certainty 

 for this purpose. Thus C. acadianum with its two to five rows, 

 C. materiarium with two, rarely three to four, rows, C. hamil- 

 tonense with two rows, and C. Newberryi with two rows, in groups 

 of six to thirteen pits, rest upon a basis which is not only easy 

 of recognition but which may be applied with full assurance. 

 In Araucaria the three species investigated may be similarly 

 differentiated from one another. The same rule is applicable to 

 Torreya taxifolia, which is thereby separable from the other spe- 

 cies; likewise to Cupressoxylon Dawsoni, Tsuga canadensis, and 

 Larix americana, and, among the pines, to P. Lambertiana, 

 P. clausa, P. Sabiniana, P. taeda, P. palustris, and P. cubensis. 

 It is to be observed, however, that the constancy which charac- 

 terizes this feature in Cordaites and Araucaria is wanting in the 

 higher Abietineae. In Larix there is such variation that very 

 careful scrutiny is required, while in the genus Pinus the num- 

 ber of exceptions to the typical character increases greatly and is 

 liable to cause some difficulty in the final determinations unless 

 much care is exercised. Pinus taeda offers a conspicuous illustra- 

 tion of this fact, as may be seen by reference to the analytical 

 key. It is therefore manifest that the value of the bordered pit 

 for taxonomic purposes is most clearly defined in the lower types 

 of the Coniferales, and that their value diminishes steadily with 



