122 VARIOUS FOOD-PLANTS 
us with energy which shall be immediately available at any 
moment for the work of life. 
45. Food-plants in general. When considering the cereal 
grains, we found that important facts regarding their special 
value and present use were explained by the original geo- 
graphical range and economic history of the species. We 
have now to conclude our study of food-plants by a com- 
parison, from this point of view, of the other kinds with 
these, so that we may arrive at some further general ideas 
concerning them. 
In the tabular view on pages 120-121 is given for each of 
the species already referred to, a brief statement of its native 
home and period of earliest cultivation, according to the 
opinion of recent authorities. Where these are doubtful 
an interrogation mark in parenthesis has been placed after 
the point in question. 
46. The primitive centers of agriculture. We have al- 
ready seen that the three grains, wheat, rice, and maize, which 
have played a supremely important part in the history of 
mankind, are each native to a region which is widely separ- 
ated from the homes of the other two,—wheat being in- 
digenous to Mesopotamia, rice to southeastern Asia, and 
maize to tropical America. 
There is abundant evidence to show that it was in these 
regions, and in the lands immediately adjacent, that agri- 
culture was first systematically pursued, and thus made pos- 
sible the development of the great civilizations of antiquity. 
It is certainly a fact of profound significance in human 
history that wheat, the most valuable of the grains, should be 
native to a region so near the junction of the three continents 
of the eastern hemisphere. Antiquarian scholars are of the 
opinion that from the fertile valley of the Tigris and Eu- 
phrates as a center, agriculture, with the civilization which 
it implies, extended to all the great peoples of Africa, Europe, 
and southern and western Asia. A more restricted civiliza- 
tion of later development and less importance was that which 
arose in the valley of the Hoangho and Yangtse-Kiang, and 
formed the beginning of the present Chinese Empire. Still 
later, although many centuries before the coming of Colum- 
