Vol. 43 TORREYA December 1943 



Criteria for the Indication of Center of Origin in Plant 

 Geographical Studies* 



Stanley A. Cain 



When the flora or fauna of any region is considered taxonomically or geo- 

 graphically, it becames apparent that it bears relationships with surrounding 

 regions. The taxonomist, phylogeneticist (if he be different from a taxonomist), 

 and the geographer are inevitably confronted by problems of origin and migra- 

 tion. 



Forty years ago Charles C. Adams pubhshed a pioneer series of papers on 

 postglacial dispersal of biota in North America (Adams, 1902a, 1902b, 1905, 

 etc.), outstanding in their conception of process in biogeography. In one of 

 these papers Adams (1902a) listed 10 criteria for the determination of centers 

 of origin, and they were later reiterated (Adams, 1909) with further com- 

 ments. Insofar as I know, these criteria have never been critically analyzed, 

 although the concept of center of origin has been attacked by Kinsey (1936). 

 Rather, they have been largely accepted without question, despite the lack of 

 substantiating data in some cases, and have been variously and somewhat 

 loosely employed. It is time for an appraisal : thus it is the purpose of this paper 

 to review these criteria in the light of more recent contributions to the science 

 of plant geography. Findings in the field of genetics, in particular, and in the 

 study of wild populations supply reasons why certain of the criteria can not be 

 tacitly accepted. 



The concept of center itself should be broken down into its various implica- 

 tions. (1) Center of origin refers only to the region in which a population or a 

 phyletic stock had its origin in an evolutionary sense. (2) Center of dispersal 

 coincides with the center of origin only for the original members of a group. 

 (3) Center of variation is the region where there is the largest number of bio- 

 types within a species, species within a section, etc. (4) Center of frequency 

 refers to the area with the densest population of the kind or kinds under con- 

 sideration. (5) Center of preservation is an area where, usually, several spe- 

 cies of a flora have survived a generally unfavorable change of environment. 

 These are the epibiotic or relic members of the flora of a region. The differences 

 among these centers are not always apparent in the literature. 



* Read at the 7Sth Anniversary Celebration of the Torrey Botanical Club at the Brook- 

 lyn Botanic Garden, Thursday, June 25, 1942. 



Contributions from the Botanical Laboratory, The University of Tennessee, N. Ser. No. 

 62. 



This paper has been shortened due to the space limitations of the Journal. A fuller treat- 

 ment of these problems may be sought in the author's "Foundations of Plant Geography," 

 to be published by Harper and Brothers. 



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