134 TORREYA 



four or more species, following the introduction of genes from all the species 

 concerned." (See also Babcock and Cameron, 1934; Goodspeed and Bradley, 

 1942.) For example, according to the studies of Camp (1942), Vacciniiim 

 corymbosum is a tetraploid hybrid complex that has no center of origin in the 

 usual sense. One contributing tetraploid was originally Ozarkian {V. arkan- 

 sanuiii), one was in the Appalachian upland (V. shnulatiun) , and one was of 

 the eastern coastal plain {V. aiistrale). 



With these qualifications concerning types of centers and with the realiza- 

 tion that under certain circumstances there may not be a center of origin, there 

 follows a consideration of the criteria proposed four decades ago by Adams. '^ 



Criterion 1. Locatiox of Greatest Differentiation of a Type 



With reference to this criterion of center of origin, Adams (1902a) says, "It 

 is a very fundamental law that most forms of life are confined to restricted 

 areas and only a small number have extensive distribution. Thus, from the 

 center of origin there is a constant decrease, or attenuation in the number of 

 forms which have been able to depart far from the original home." 



This criterion is legitimate and applicable if we make two assumptions. In 

 the first place, the basic assumption underlying the whole thesis is that there is a 

 center of origin for a phyletic stock. This has already been discussed in the in- 

 troduction. The other assumption is that there is a time relationship in evolu- 

 tion, that polymorphism increases with time ; and that there is an age-and-area 

 relationship, that with age the population of a species or other group tends to 

 increase and occupy a wider area. In this connection see Willis (1922, 1940) 

 and the numerous expert criticisms of his hypothesis. If we can accept these 

 assumptions, it is clear that there will tend to be more polymorphism in the 

 region of origin of a phyletic stock than away from this center. In such a region 

 there will be more forms (biotypes, subspecies, species, sections, etc.) because 

 of the longer time in which evolution has been occurring in the steadily increas- 

 ing numbers of different kinds. With time, some of the forms originating in the 

 central region will attain wider areas. They, in turn, may give rise to new forms 

 away from the center, but in the nature of the relationship, the original area 

 will tend to exceed any derived peripheral area in the number of kinds repre- 

 sented. 



^ I wish it understood that the evaluation of them is in no way a specific attack on 

 Adams' paper, which was breaking new ground at that time, but is rather a criticism of 

 the present day employment of these rules without evaluation of them in the light of more 

 modern knowledge, and recognition of their limitations. As a matter of fact, by 1909 Adams 

 was careful to point out that he understood the criteria to be only "convenient classes of 

 evidence to which we may turn ... It should be clearly emphasized that it is the conver- 

 gence of evidence from many criteria which must be the final test in the determination of 

 origins ..." 



