MODIFICATION AND DISTRIBUTIONS OF CROPS 23 1 



considerably in excess of that of the Potato. Yet under suitable 

 conditions of moist climate and rich but light soil, the Potato is 

 able to supply considerably more human food per unit area than 

 any of the cereals, the world crop during 1934-38 being produced 

 by about 22 million hectares as opposed to an estimated 168 million 

 hectares under Wheat. Relatively to the following two so-called 

 ' root ' crops, the Potato is hardy, especially in some of its numerous 

 forms. Fig. 70, A, indicating most of its cultivated range in the world. 

 In addition the present writer has eaten quite large home-grown 

 Potatoes in central Alaska and far down the Mackenzie Valley, and 

 small ones in southern Greenland and in northernmost Scandinavia 

 near 71° N. lat. He has even eaten tiny ones much farther north 

 in Spitsbergen, grown on the pyre of a burned-out hut. In the 

 White Potato the storage tuber is really an underground stem 

 structure bearing buds (the so-called ' eyes '). 



The Sweet Potato {Ipomoea batatas), an ancient crop of tropical 

 America, is now widely cultivated in the warm parts of the world, 

 being in fact a standard article of food in practically all tropical 

 and subtropical regions. It requires a sandy soil and a moist climate 

 for successful growth. Another very important tropical food plant 

 of this nature (though actually shrubby) is the Cassava {Manihot 

 esculenta), which originated in South America in prehistoric times. 

 It can be cultivated in hot, seasonally arid climates where cereals, 

 etc., will not grow. Its many varieties now furnish the basic food 

 for millions of people, particularly in Central and South America, 

 and also supply the world with tapioca. 



Other important ' root ' crops which are widely used as vegetables 

 include various types of Yams {Dioscorea spp.) in warm regions, and 

 Turnips and Rutabagas (Swedes) which are also used for animal 

 feed particularly in temperate regions. There are also Beets {Beta 

 vulgaris) and Carrots (Daucus carota), which both succeed under a 

 wide range of climatic and soil conditions. Beets were domesticated 

 first as a leaf vegetable, then as root crops, and finally as a source 

 of sugar {cf. upper part of Fig. 75) ; they are probably derived 

 from one variable species that is native in the Mediterranean region. 

 Carrots are likewise of ancient origin, various form, and now very 

 widespread cultivation. 



(3) Other Vegetables — This somewhat vague category includes 

 some structures (such as Tomatoes and the pods of Beans) which 

 technically are fruits. Examples are the Broad Bean {Vicia faba), 

 which is one of the world's commonest and most important beans 



