GEOGRAPHICAL DISTRIBUTION 151 



chiefly by mammals such as oaks, beeches, hazels, 

 crabs, etc. are entirely wanting. 1 It has been suggested 

 by both Guppy and Schimper that the wide distribution 

 of fig trees in oceanic islands (e.g. Malay and Solomon 

 Archipelagos) is due to their fruit being eaten by doves 

 and other birds capable of sustained flight. The pro- 

 digious powers of flight of some of the migratory birds 

 would make them, theoretically at least, most efficient 

 agents of seed dessemination over wide areas. The scarlet 

 tanager, for example, breeds in the eastern United States 

 from Oklahoma to the mountains of North Carolina, and 

 north to New Brunswick and Saskatchewan. At the 

 close of summer the birds migrate south, passing from 

 the Gulf coast of the United States to and along Central 

 America to the west tropical coast of South America. 

 The arctic tern nests during the northern summer along the 

 northeast arctic coast of North America ano! the southwest 

 coast of Greenland, but passes the northern winter within 

 the Antarctic Circle, 11,000 miles away. Passing as it 

 does through regions of similar climate in the northern 

 and southern hemispheres, it would theoretically be 

 possible for spores and light seeds to be carried to con- 

 genial habitats on both sides of the equator. The 

 American golden plover breeds in summer along the 

 northern coast of Canada, the parallel of 70 north latitude 

 passing approximately through the center of its breeding 

 range. In early fall the birds migrate to Labrador, 

 thence to Nova Scotia, and thence, after a few weeks, 

 in a straight flight of 2,400 miles to the north coast of 

 South America. From their landing point the birds 

 pass to Argentina where they pass the northern winter, 



1 Wallace, A. R., Darwinism, 3d edition, p. 361. 



