BORDERED PITS 77 



representative than any species now existing, and that it is sub- 

 stantially the ancestral form of the genus, so far as we know. 



In Larix the four investigated species may be differentiated 

 pretty fully, and this rule applies with particular force to L. 

 americana and L. occidentalis, both of which are distinguished 

 by two-seriate forms. Among the pines P. Lambertiana, P. clausa, 

 P. Sabiniana, P. taeda, P. palustris, and P. cubensis are readily 

 differentiated from the others by the two-seriate pits. In all 

 other cases than those specifically indicated the bordered pits 

 afford an inadequate basis for specific differentiation. 



It is now apparent that segregated round or oval pits in one 

 row must be taken as representing the highest type of develop- 

 ment in the Coniferales, and any deviation from this must be 

 taken to indicate the survival of more primitive conditions, 

 pointing to derivation from a type like that of Araucaria or 

 Cordaites. From this point of view the occurrence of pits in 

 one-to-two rows in Larix americana, Torreya taxifolia, Sequoia, 

 Tsuga canadensis, and various species of Pinus indicates the 

 survival of ancestral characters which are partial to the extent 

 of 7.2 per cent, and complete to the extent of 10.8 per cent. 

 That such deviations from the usual type of structure are either 

 survivals or reversions which serve to indicate a common origin 

 cannot be doubted, more especially as they do not occur at a 

 fixed point near the original type, but they arise sporadically 

 in widely separated genera. The tendency of such evidence, 

 then, is to show a common ancestry for the various genera of 

 the Taxaceae and Coniferas, a view which is greatly strength- 

 ened by the testimony afforded by the spiral tracheids of Larix 

 americana, Pseudotsuga, and Pinus taeda. 



