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TEXTBOOK OF BOTANY 



them. Compare, for instance, our present varieties of cabbage, kohlrabi, 

 cauHflower, kale, and Brussels sprouts with the mustard-like wild an- 

 cestor from which these cultivated varieties were derived (Fig. 196). 



Fig. 196. Domesticated varieties derived from the wild cabbage, Brassica oleracea 

 (A), a native of Europe. B is kale, Brassica oleracea acephala; C, kohlrabi, B. 

 oleracea caulo-rapa; D, Brussels sprouts, B. oleracea gemmifera; E, pointed-head 

 cabbage, B. oleracea capitata; F, round-head cabbage, B. oleracea capitata; G, cauli- 

 flower, B. oleracea botnjtis. 



The wild ancestors of the domesticated plants of Eurasia are better 

 known than those of America. Com is the only important cereal that 

 originated in America. Its wild ancestor was a grass; but in spite of a 

 prolonged search for this grass, it is still unknown today. 



When Columbus arrived in America, the Indians of the New World 

 were cultivating several distinct varieties of corn, potatoes, sweet po- 

 tatoes, kidney and lima beans, peanuts, pumpkins, squash, tomatoes, 

 pineapple, pepper, arrowroot, sunflower, Jerusalem artichoke, beach 

 strawberry, tobacco, cotton, and many other plants (Fig. 197). These 

 plants were domesticated by prehistoric man in the highlands of Mexico, 

 Central America, and the northwestern part of South America: the 

 regions in which the Incas, Mayas, and Aztecs later developed their 

 remarkable civilizations. Previous to the voyage of Columbus none of 

 these domesticated plants of America was known in Europe, and none 

 of the domesticated plants of Europe was known in America. Within 

 each hemisphere, however, several important crop species had become 

 widely distributed. The Indians were cultivating corn in many local 



