CAIN: CENTER OF ORIGIN 151 



"proportionally to the spread of isolation, proceeds the accumulation of reces- 

 sive forms." 



Criterion 13. Center Indicated by the Concentricity of Progressive 



Equiformal Areas 



This criterion, developed by Hulten (1937), primarily concerns centers of 

 dispersal for arctic and boreal biota from refugia ; but it also concerns centers 

 of origin when evolution as well as migration has occurred. Hulten's thesis is 

 as follows : from a refugium, each species tends to spread in all available direc- 

 tions, but because of different tolerances and capacities for dissemination it 

 could not be expected that all plants would spread to the same extent or with 

 the same rapidity. The result is a tendency toward the development of approxi- 

 mately circular areas of different size around the center ; but in nature the 

 theoretically circular form of areas is seldom attained because of various bar- 

 riers. There still remains, however, the chief feature of areas : those plants that 

 radiate from the same center have progressive equiformal areas of different size. 

 This criterion is obviously related to number six stated by Adams. As developed 

 by Hulten, however, there is a clean-cut scientific basis with the conclusion 

 reached through strictly inductive reasoning. 



Conclusion 



There seems to be only one conclusion possible, and it carries implications 

 far bcA'ond the scope of the present discussion of criteria of center of origin. 

 The sciences of geobotany (plant geography, plant ecology, plant sociology) 

 and geozoology carry a heavy burden of hypothesis and assumption which has 

 resulted from an over-employment of deductive reasoning. What is most needed 

 in these fields is a complete return to inductive reasoning (Raup, 1942) with 

 assumptions reduced to a minimum and hypotheses based upon demonstrable 

 facts and proposed only when necessary (Hulten, 1937). In many instances 

 the assumptions arising from deductive reasoning have so thoroughly permeated 

 the science of geography and have so long been a part of its warp and woof 

 that students of the field can only with difficulty distinguish fact from fiction. 



The University of Tennessee 

 Knoxville, Tennessee 



Literature Cited 



Adams, C. C. 1902a. Southeastern United States as a center of geographical distribution 



of flora and fauna. Biol. Bui. 3: 115-131. 

 . 1902b. Postglacial origin and migrations of the life of the northeastern United 



States: Jour. Geogr. 1 : 303-310 ; 325-357. 

 . 1905. The postglacial dispersal of the North American biota. Biol. Bui. 9: 53-71. 



