22 BIOLOGICAL PROBLEMS 



were familiar to prehistoric man ; wheat, for instance, 

 was probably used for food long before the remote 

 period when it was carefully cultivated by the ancient 

 Egyptians and the early Chinese. 



Throughout the historical period, and probably for 

 longer, agricultural mankind has expended its skill 

 and effort on two main cereal crops. Rice and wheat 

 are, and always have been, the great cultivated crops 

 of the world. Important as are oats, barley, and 

 maize, they have never formed the basal food of 

 really large communities. Climate and racial tastes 

 or capacity have determined whether wheat or rice 

 should form the basal food of a nation. Rice gives a 

 much larger yield per acre, but it makes more demands 

 upon climate than does wheat, and its culture is a 

 more difficult art. The temperature during its six 

 months of growth must reach 70 F. or upwards, 

 and its need for abundant water, supplied always at 

 the right time, calls for special geographical con- 

 ditions as well as constant attention. Wheat can be 

 grown within a wider range of climatic conditions, 

 and its culture calls for less meticulous attention. A 

 much smaller proportion of a population depending 

 upon it need be concerned in its actual cultivation, 

 and, unlike rice, it can be produced so as to be greatly 

 in excess of local needs. Wheat, therefore, bulks 

 largely in international trade, and industrial com- 

 munities can always, when transport is available, 

 obtain their supplies from fields far distant. Rice is 

 eaten, so to speak, on the spot. Of the vast world har- 

 vest of this cereal only a minute fraction travels over- 

 seas. Wheat, as stated, can suffer very considerable 

 varieties of climate, but the character of the climate 

 and of the soil where it is grown affect the characters 

 of the grain, a fact which, as we are to seej has had 

 interesting and important economic consequences. 



