No. 448.] A ORTH AMERICAN CONIFERALES. 255 



pact spirals of Taxus. This fact, so far as it possessed phylo- 

 genetic value, appears to confirm the conclusions as to the rela- 

 tive positions of these two genera, already determined upon the 

 basis of external morphology as stated by Eichler (11, p. 108). 



It has already been made clear from the preceding facts, as 

 well as from former discussions (40, p. 56) that in the case of the 

 Taxacese and also of Pseudotsuga, the spirals must be regarded 

 as a survival of primitive structures. On a former occasion 

 (40, p. 57) I was inclined to consider that their occurrence in 

 Larix and Finns heda was atavistic, but in the light of more 

 recent evidence as now set forth, this opinion requires modifica- 

 tion in so far as to include the idea that they do not express 

 mere parallelisms in development, but that they afford evidence 

 of a common ancestral type at some point far anterior to the 

 evolution of the Taxaceae. We must therefore consider that 

 Torreya, Taxus, Pseudotsuga, I.arix and Pinus represent differ- 

 ent branches of a general phylum — undoubtedly including also, 

 other closely related genera in which the spirals have been 

 wholly obliterated — which had its origin at a point anterior 

 even to such types as Cordaites, and therefore, in all probability 

 in what Coulter (7) has very happily designated as " the great 

 Cordaitean plexus " arising from the eusporangiate ferns, or 

 what, according to our more recent knowledge, and Coulter's 

 more recently expressed view (8, p. 172) would be designated as 

 the Cycadofilices. 



Bordered Pits Distribl-iiox and Stkucti rk. 



In the preceding pages, the derivation of the bordered pit from 

 the spiral tracheid, and its obviously more intimate relation to a 

 higher type of development have been made clear. Our j^resent 

 purpose is to discuss these structures with special reference to 

 (i) occurrence, (2) distribution, (3) structural modifications, {4) 

 taxonomic value and (5) their value as evidences of descent. 



At the outset, reference may be made to the occurrence of 

 bordered pits on the radial walls of the ray cells as exhibited 

 typically in Sequoia and Taxodium. Their location in such situa- 



