CHAPTEK VII 

 THE PHYLOGENY OF GYIXNOSFEBIVIS 



Any statement as to the phylogeny of a group must be largely- 

 hypothetical. The data upon which opinions are based are 

 never sufficient, but such opinions serve to coordinate knowl- 

 edge and to suggest proiitable research. Only a small fraction 

 of living forms have been studied adequately ; while the extinct 

 forms, which represent the early history essential to phylogeny, 

 will probably never be known except in an uncertain and frag- 

 mentary way. In the case of Gymnosperms we have the advan- 

 tage of dealing with a woody group, whose fossil remains may be 

 taken to represent their ancient history with unusual complete- 

 ness. But even in the presence of an abundance of remains, the 

 facts of greatest service to morphologists are for the most part 

 inaccessible. 



Before suggesting a possible phylogeny for the group and 

 its various members, it may be well to state certain factors 

 which must enter into any consideration of such a subject. In 

 the first place, it should be remembered that it is exceedingly 

 improbable that any important group of living forms has been 

 derived from another group of living forms. Eescniblances in 

 structure which are regarded as essential may be pointed out, 

 but this is not likely to mean the origin of one group from the 

 other; it may mean that the two groups can be traced to one, 

 probably now extinct, which combines the characters now dif- 

 ferentiated. Most living groups are best regarded as divergent 

 rather than consecutive series. 



Another important point is that similar changes in structure 

 may have appeared independently in different lines. The re- 

 sponse of organisms in their structure to environment is deeper 

 seated than we were once inclined to believe, and testimony 

 from the similarity of certain structures, when contrary to the 

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