128 ADAMS. 



5. The geographical distribution of color variations is a subject 

 which it is very desirable to study from the standpoint of geo- 

 graphic origin as well as from that of climatic influences. Allen 

 ('71, '72, '74, '77 and '92), especially, has given much attention 

 to the formulation of the laws of geographic color variation 

 among North American birds and mammals, and correlates some 

 of these variations with that of moisture. Ridgway ('72) has 

 also an important paper on color variations in birds. Keeler 

 ('93) and Hasbrouk ('93) are referred to for further information 

 on color variations. These papers give numerous cases showing 

 that species of wide distribution change in color in different 

 localities. These papers cannot be discussed here, but deserve 

 to be much better known. 



SUMMARY. 



First. In general the fauna and flora of Northern United 

 States East of the Great Plains are geographically related to those 

 of the Southeast and this geographical relationship points to an 

 origin in the direction of the Southeast except in the case of the 

 distinctly boreal forms. 



Second. The abundance and diversity of life in the Southeast 

 indicates that it has been, and now is, a center of dispersal. 



Third. The relicts indicate that the Southeast has been a 

 center of preservation of ancient types, and the endemism shows 

 that it has been a center of origin of types. 



Fourth. There are two distinct Southern centers of dispersal 

 in temperate United States ; one in the moist Southeast, and the 

 other in the arid Southwest. 



Fifth. Ten criteria, aside from fossil evidence, are recognized 

 for determining the center of origin or the locality of dispersal : 



1 . Location of the greatest differentiation of a type. 



2. Location of dominance or great abundance of individuals. 



3. Location of synthetic or closely related forms. (Allen.) 



4. Location of maximum size of individuals. (Ridgway, 

 Allen.) 



5. Location of greatest productiveness and its stability, in 

 crops. (Hyde.) 



6. Continuity and convergence of lines of dispersal. 



