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PLANT PHYSIOLOGY AND ECOLOGY 



of evolution, the theory of single origin was retained. This was 

 in spite of the fact that almost insuperable difficulties were often 

 found in trying to explain through migration the presence of the 

 same species in two or more remote and isolated regions. 



The view that the same species may arise at different places or 

 times has recently been maintained by several ecologists.i It is 



Fig. 71. The mountain fringed gentian, Gentiana amarella, illustrating 

 polygenesis. The first dwarf grew in alpine gravel at 3700 m., the 

 second in subalpine gravel at 2800 m. and only a few inches from the 

 normal many-flowered form. 



at once evident that this may occur in the case of hybridation 

 whenever the parents are spread over a wide area. The experi- 

 ments of De Vries and his followers upon (Enothera have proved 

 that the same mutant may arise at remote places as well as at 



> Research Methods, 230. 



