INTRODUCTION 1 3 



as anatomically identical with P. contorta, as suggested by Sar- 

 gent, for the same reasons as already applied to Pseudotsuga. 

 Similarly P. Jeffreyi is a valid species and P. ponderosa scopu- 

 lorum must be raised to the position of a species, while yet others 

 fall into the same category. 



The sequence of genera and species, as well as the relations 

 of the larger groups, is based upon the anatomical data presented 

 in Part I, and it will be found to deviate considerably from most 

 of the systems of classification now in use. In exhibiting this 

 sequence, which appears abundantly justified from one point 

 of view, it must nevertheless be carefully kept in mind that 

 such an arrangement is in no sense regarded as final. At best 

 it is a purely tentative measure, which shall serve as a contri- 

 bution toward a final classification, and this latter can be com- 

 pleted only when data from several sources are assembled and 

 coordinated. 



As derived from our present studies the sequence of the 

 Gymnosperms may be stated as in table on the following page. 



With respect to fossil forms an effort has been made to include 

 all known North American species so far as they have been 

 recognized through the structure of the wood alone. These have 

 been included under their respective genera as now known for 

 existing species, and thus Cupressinoxylon 1 or Cupressoxylon are 

 described under Cupressus, while Pinoxylon and Pityoxylon fall 

 under Pinus. Unfortunately, in most cases, it is not possible to 

 determine the structural characters with that detailed thorough- 

 ness which is desirable, owing to the imperfect nature of the 

 material, and it has therefore been found necessary to arrange 

 the fossil species in a separate section of the genus and provide 

 separate analytical keys. The very great difficulty of obtaining 

 full differential characters necessitates reference to type speci- 

 mens whenever a serious doubt arises. In several cases the 



1 The genus Cupressinoxylon, as elsewhere shown, embraces what may prove 

 upon revision of existing descriptions Sequoia in some cases and Cupressus 

 in other cases, while according to Jeffrey's latest publications he employs the 

 term for fossil Sequoias. Provisionally I prefer to include it under the genus 

 Cupressus. 



