CHAPTER VII 

 THE PHYLOGENY OF GYMNOSPERMS 



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 profitable 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 

 inipr^bable_that_any important group of living^ forms .hasjbe_en 

 derived from anotErgroiTpIHIiESTig -Fnrrng" Resemblances 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 pointjsJJial similaj^chariges in structure 

 may have appeared independently in different lines! The re- 

 sponse oTofgamsms 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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