DISTRIBUTION OF FLORA AND FAUNA. I I/ 



United States is a center of dispersal, yet one can hardly doubt 

 that such will prove to be the case, upon investigation. The 

 annual paths of bird migrations favor this idea. One more illus- 

 tration will be taken from the fauna. Mr. Bryant Walker's ('98, 

 p. 10) study of the Unionid fauna of Michigan clearly shows that 

 this fauna is almost entirely of Mississippi River origin, and the 

 Mississippi River Unionid fauna is well known to be of south- 

 eastern origin. But it is not necessary to multiply instances, be- 

 cause the same law holds for the bulk of our fauna and flora and 

 will be recognized by one familiar with any fairly large group of 

 animals. The affinities of both fauna and flora thus point to, 

 and converge toward the Southeast. About the only marked 

 exceptions to the rule are the distinctly northern or boreal groups. 

 Such illustrations as the foregoing are significant and sufficient 

 to show that to the Southeast is a region deserving of special at- 

 tention from a faunal standpoint. Because it is believed that here 

 is the natural starting point for an attempt to untangle many 

 faunal and floral problems, evidence has been collected which 

 seems to throw light upon some of its peculiarities. 



RICHNESS, OR ABUNDANCE AND DIVERSITY OF LIFE. 



As an illustration of the abundance of life, I will consider the 

 flora, which shows a luxuriant development. Sargent ('84, p. 4) 

 says : " Upon the slopes of the southern Allegheny Mountains, 

 and in the valley of the lower Red River, regions of copious rain- 

 fall and rich soil, the deciduous forest of the continent attains 

 unsurpassed variety and richness." 



The richness of the fauna is shown by both the abundance and 

 size of the individuals. Binney ('85, p. 34) has called attention 

 to this in the case of the land shells of the " Cumberland Sub- 

 region " of the southern Appalachians. He says : " If to the 39 

 species catalogued above as peculiar to this subregion, are added 

 the 69 which inhabit it as a portion of the interior region, it is 

 seen that in the Cumberland subregion we find the largest num- 

 ber of species of any portion of North America. The subregion 

 is equally prolific in individuals, and the individuals are highly 

 developed." 



The fresh water molluscan fauna is even richer than the land 



