MODIFICATION AND DISTRIBUTIONS OF CROPS 229 



before the period of the Inca civihzation. Radiocarbon determina- 

 tions of primitive cobs found in Bat Cave in New Mexico, indicate 

 that this material was between 5,000 and 5,600 years old.' In spite 

 of its numerous forms, Maize is a crop mainly of rather exacting 

 requirements of considerable summer moisture in warm countries. 

 It does not ripen far north ; indeed not many regions have the 

 right combination of environmental conditions for the raising of 

 Maize on a large scale. Most notable is the eastern half of the 

 United States, which produces about half the world's crop, although 

 there are other considerable centres of production in South America, 

 southern Europe, and eastern Asia, as indicated in Fig. 69. Maize 

 is used principally for feeding Hogs and other domesticated animals, 

 but is also favoured as a vegetable. 



The various types of Millets, belonging to several different genera 

 of Grasses, and the Sorghums, belonging to the genus Sorghum, should 

 also be mentioned as widely grown for forage, grain, and many 

 other purposes. The Sorghums have been cultivated in Asia and 

 Africa since very early times, constituting a staple food for millions 

 of native peoples. Latterly they have come to be grown in other 

 tropical and warm-temperate regions, being particularly useful 

 because of their ability to grow under dry conditions and actually 

 withstand droughts. 



(2) ' Root ' Crops — Of these the Irish or White Potato [Solaniim 

 tuberosum) is the most widely important, having no rival as an 

 efficient producer of food, especially in relatively moist and cool 

 countries. Although the Potato's origin lay in the mountainous 

 portions of South America, over 90 per cent, of world production 

 is now in Europe, whose population has increased substantially as 

 a result of its cultivation. In comparison with the other leading 

 food-crops, the average annual world production during 1934-38,^ 

 expressed in millions of metric tons, has been estimated as approxi- 

 mately 233 for Potatoes, 167 for Wheat, 152 for Rice, 115 for Maize, 

 65 for Oats, 52 for Barley, and 47 for Rye. Actually these figures, 

 although interesting, are only fragmentary for some crops, and are 

 moreover misleading in that Potatoes contain at least 78 per cent, 

 of water, against an average of only about 13 per cent, for cereals. 

 Consequently, the actual dry-weight food production of Potatoes in 

 that period was only about 51 million tons, whereas for Wheat it 

 was approximately 145 million tons, and for Rice and Maize also 



* The last period for which the F.A.O. Yearbook (vol. IX, part i, 1955) gives 

 pertinent statistics for the U.S.S.R. 



