CAIN : CENTER OF ORIGIN ' 149 



ing a temperate origin because of a few temperate representatives, as in 

 Diospyros, Tripsacum, and Phoradendron, but quite the contrary. The point 

 is well illustrated by a quotation of Merrill (1936). "When a genus is described 

 from material collected in a certain place and is known only from that region 

 for many years, we more or less automatically accept it as a group characteristic 

 of that region. If a representative of it is later found in another area, we are apt 

 to consider it as an extraneous entity there." 



Returning to our own region we can cite an example. Typical Atlantic and 

 Gulf coastal plain species have long been known from the Appalachian and 

 Cumberland uplands (Gattinger, 1901; Kearney, 1900). Sometimes these in- 

 land plants are rare, and stations are of small area and widely disjunct from 

 the coastal plain where the species are now common. Fernald (1931) has cor- 

 rectly hypothesized the origin of some of these species on the old lands that 

 are now part of the Cumberland plateau, and Braun (1937a, 1937b) has found 

 them most abundantly in the undissected portions of the now elevated peneplain. 

 Fernald says, "With the Tertiary uplift of the Appalachian region and its final 

 conversion into a vast well-drained mesophytic area . . . the Cretaceous xero- 

 phytes and hydrophytes which had previously occupied the ground gradually 

 moved out to the newly available and for them more congenial Coastal Plain 

 and similar habitats to the west and northwest." In such a case as this, the prin- 

 cipal area is a derived one and is no indication of the center of origin. It really 

 is not a question of coastal plain plants in the Appalachian and Cumberland up- 

 lands, but of upland plants in the coastal plain, if we view the relationship his- 

 torically. Not all coastal plain species in the interior have had this history. In 

 his monographic study of the Scrophulariaceae, Pennell (1935) has detected 

 some forms that have migrated from the coastal plain into the Piedmont and 

 the Blue Ridge provinces.?. 



The direction of dispersal and the center of origin are many times indicated 

 by geographical affinities, but the criterion can not be used alone, and the prihci- 

 pal area and biographic type may be derived and the minor area relic. 



Criterion 10. Direction Indicated by the Annual Migration Routes, 



IN Birds 



Applied to plants, this criterion would be restricted to species whose dia- 

 spores are bird disseminated, either epizooically or endozooically. If the migra- 

 tion takes place both northward and southward over the same route, as for 

 some species employing the Mississippi valley and others using the Appalachian 

 uplands, direction of plant movement is not necessarily indicated. In cases 

 where the northward and southward migration paths are not coincident, the 

 direction of movement is indicated. 



