462 OEIGIN OF CULTIVATED PLANTS. 



perhaps as far as America, do not seem to have trans- 

 ported a single cultivated species. Neither has the Gulf 

 Stream produced any effect. Between America and 

 Asia two transports of useful plants perhaps took place, 

 J the one by man (the Batata, or sweet potato) the other 

 ) by the agency of man or of the sea (the cocoa-nut palm). 



