CHAPTER XX 

 PHYLOGENY 



Throughout the preceding chapters, remarks have been made and 

 opinions have been expressed in regard to the relationships of various 

 groups; but it seems best to assemble some of the scattered views, 

 add some arguments, and to consider the evidence upon which 

 botanists founded their theories of phylogeny.* 



Similarity of structures has been relied upon in all attempts to 

 arrange plants in a natural, or genetic, sequence. Morphologists of 

 the older school believe that most of this evidence, especially that 

 afforded by embryology, is reliable; modern morphologists believe 

 that some of this evidence, but not so much of it, is due to genetic 

 relationship. There are ecologists and physiologists who would go 

 still farther and claim that external form and internal structure are 

 due, almost entirely, to environment and function. 



Heredity and environment determine the form, structure, and 

 life-history of a plant. Morphologists have overemphasized the 

 influence of heredity, while ecologists and physiologists have over- 

 emphasized the influence of environment. 



It is becoming more and more evident that some of the things 

 which have been attributed to heredity may be due to environment ; 

 but, as an acute observer remarked some 2,000 years ago, you do not 

 gather figs from thistles; and very probably, if there had been con- 

 stant experimentation from that time up to the present, not a single 

 member of the fig family could have been transferred to the sun- 

 flower family. However, it must be recognized that there is such a 

 thing as ecological anatomy, and also that phylogenetic anatomy is 

 equally important. When pumpkin seeds and corn are planted in 

 the same hill, the phylogenetic factor determines that one shall pro- 

 duce pumpkins, and the other, corn. Physiological and ecological 



* Some of the views, expressed in this chapter, even with their phraseology, were pre- 

 sented in a symposium before the International Congress of Plant Sciences, at Ithaca, 

 New York, August 19, 1926."'' 



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