CAIN : CENTER OF ORIGIN 135 



A few quotations will illustrate this point. Payson (1922) says, "There 

 is much evidence for believing that Lesquerella originated at some point in 

 Central Texas and from this point as a center has spread over the large area 

 that it now occupies . . . From purely theoretical standpoints also, the greatest 

 number of species might be expected to occur in the vicinity of the point of 

 origin, since there the genus would have existed for the longest period of time." 

 In a recent publication on Ceanothus, Mason (1942) says, "The occurrence of 

 many isolated local species along the coast as against a few widespread species 

 of the interior would indicate that the direction of the Ceanothus migration was 

 from the coast to the interior." 



Another example of the use of this criterion, which also is admirably sup- 

 ported by phylogenetic and geological data, is the study of Gaylussacia by Camp 

 (1941). He says, "it becomes apparent that the genus arose in South America 

 for there, today, we find it as a series of interlocked species-groups still diflfer- 

 entiating out of a common plexus, only three of which have given representative 

 members to North America." The work of Szymkiewicz (1937) indicates a 

 concentration of Mediterranean species ot various genera, especially endemic 

 species, in western Mediterranean regions. One example of this type will be 

 sufficient. Sirjaev (1934) has carefully mapped the distribution of the members 

 of the Mediterranean genus Ononis and makes the following statement con- 

 cerning center of origin : "Das Entstehungszentrum der Gattung {Ononis) war 

 wahrscheinlich auf der Iberischen Halbinsel und im nordwestlichen. Mediter- 

 ranen Afrika, wo jetzt noch alle Subsektionen und viele endemische und fast 

 alle alteren Arten sich konzentrieren, wahrend im ostlichen Teile des Medi- 

 terraneums keine eigene Subsektion und nur drei endemische Arten anzutreffen 

 sind . . . Die Migration aus dem Entstehungszentrum fand in verschiedenen 

 Epochen auf verschiedenen Wegen Statt." The investigations of Van Steenis 

 (1934-1936) on isoflors (lines connecting regions of equal numbers of species 

 in a genus) offer another method in which a strong indication of center of 

 origin is obtained. Perhaps the most intensive studies of plants and their centers 

 ever made are those of Vavilov (1940) and his colleagues. The following quo- 

 tation is pertinent : 



"Cultivated species as well as their closely alHed wild relatives in their evo- 

 lution, during the course of their distribution from the primary centers of spe- 

 cies-formation, have been dififerentiated into definite ecological and geographical 

 groups . . . Primary regions are at present characterized, as a rule, by the pres- 

 ence of many different species (in the sense of Linnaeus). They reveal prac- 

 tically the entire systems of genera." 



It is necessary, however, to recognize that this criterion can not be accepted 

 as universal, for it only describes a tendency that, under certain conditions, is 

 counteracted by the operation of other factors, as is also true of age-and-area. 

 A few of these conditions will be described. 



