BORDERED PITS 75 



given, and that the sequence of species must be approximately 

 as given in the table of anatomical data. 1 



The observations so far made apply altogether to the pits on 

 the radial walls. We may now pass to a consideration of their 

 relation to the tangential walls, a factor which does not call for 

 very extended discussion. This feature is found to apply to 

 71.7 per cent of all investigated species exclusive of fossils. 

 It is wanting in three species of Araucaria, representing 2.58 

 per cent ; in two species of Torreya, or 1.72 per cent ; and in the 

 entire second section of Pinus to the extent of twenty-eight 

 species, or 24. i per cent. But the occurrence of pits on the 

 tangential walls, in common with those on the radial walls, is 

 a well-known feature of the Sigillarias (81, 198), where their 

 primitive character is well established, and we can hardly doubt 

 that their final elimination in the higher pines is the expres- 

 sion of a final phase in development consistent with the position 

 usually assigned those plants. 



The absence of pits from the tangential walls of certain 

 Araucarias and Torreyas is to be interpreted as one of those 

 sporadic tendencies toward a higher type of development which 

 never become permanent in the same line, but which are to be 

 met with as one of the invariable features of evolution. 



The remaining genera of the Coniferales present so few devia- 

 tions from a typical form that they cannot be differentiated 

 fully on the basis of the bordered pits. This character never- 

 theless has a definite value in association with others, as in the 

 genus Sequoia or some of the hard pines, Larix americana, etc. 

 The general sequence of genera may be recognized by the bor- 

 dered pits only in so far as these structures serve to confirm 

 and emphasize the conclusions reached in other ways, and this 

 will become apparent from an inspection of the table already 

 referred to. It will nevertheless serve a useful purpose at the 

 present moment to ascertain the general sequence based upon 

 the percentage distribution of the principal variants, as seen by 

 the table on following page. 



1 Appendix A. 



