72 ANATOMY OF THE GVMNOSPERMS 



an advance towards higher forms of organization and develop- 

 ment. In all cases where exceptional forms introduce diagnostic 

 difficulties these may be overcome by the controlling effect of 

 associated characters. 



We are now in a position to examine the data at hand with a 

 view to determining the bearing of the bordered pits upon ques- 

 tions of phylogeny. 



Having reference to the origin of the bordered pit and the 

 various modifications it presents in the course of development, 

 it cannot be doubted that the hexagonal, multiseriate pits of 

 Cordaites, Araucarioxylon, Araucaria, and Dammara place these 

 genera in a relatively inferior position, --a view which gains a 

 large measure of support from the well-known and extensively 

 multiseriate disposition shown in Heterangium Grievii (81, 341), 

 but the facts so far discussed have not as yet thrown any special 

 light upon the relative positions of the separate genera. 



An examination of twelve species of Cordaites shows that the 

 bordered pits exhibit a much wider range of serial variation than 

 any other genus covered by the present studies. If then we 

 accept the general principle with respect to the development of 

 the bordered pits as already illustrated, it cannot be doubted that 

 the two- to five-seriate pits stand much nearer to the primitive 

 form of the tracheid than do the one-seriate. From this point 

 of view it is then evident that in C. recentium, the name of which 

 is thereby seen to be fully justified, the one-seriate pits place it 

 at the upper end of a series which has its inferior termination in 

 the two- to five-seriate C. acadianum, while intermediate forms 

 appear between the two as members of a series of nine variants, 

 and it is possible to arrange these in such a manner as to exhibit 

 the probable sequence in development, as seen by table on the 

 following page. 



The wide range of variations here shown, especially when 

 compared with other genera, at once serves to suggest that 

 Cordaites was in this respect somewhat of the nature of a tran- 

 sition group from which others were given off, or else that it 

 epitomized the collective changes through which a number of 



