50 TILLERS OF THE GKOUND CHAP. 



CHAPTEB V 



THE SPREADING OF FOOD-PLANTS 



WE have seen already that the last two thousand 

 years have not added a great many to the number 

 of food-plants known. In the Old World at least, 

 not only was the work of selecting suitable food- 

 plants nearly completed before this, but also the 

 known plants were widely distributed in nearly all 

 suitable places. America was an exception, for till 

 its conquest by the Spaniards there does not seem 

 to have been any interchange of plants between 

 the Old World and the New. After its discovery 

 not only were a few useful American plants intro- 

 duced into Europe and Asia, but many useful Old 

 World plants were introduced into America. That 

 country indeed received far more than she gave, 

 and this is one reason why, though the old America 

 could barely feed her own scanty population, the 

 America of to-day pours a ceaseless stream of food 

 into Europe. The Old World gave to the New out 

 of its store of knowledge and experience in the 

 form of useful plants, and it is every day receiving 

 back its gift a thousandfold. 



This interchange of plants between the Old and 



