PREFACE 



The feeding of future generations requires a knowledge of the 

 individual crop plants of the world and their potentials. Crops can 

 be recommended for particular regions only on the basis of poten- 

 tial yield, the costs of production, the food and feed value of the 

 crop, and the way the crop can be processed or otherwise used. 

 For most of the major food crops of the world, a body of informa- 

 tion is available. However, tropical roots and tubers, which are 

 widely used as staple foods, have been largely neglected. Only in 

 recent years has an awareness been growing of the potential of 

 these crops to supply large amounts of food in relatively small 

 amounts of space. 



Yams are the second most important tropical root, or tuber, 

 crop. The annual production, perhaps 25 million tons, places them 

 second in importance to cassava. But yams are better food than 

 cassava, and although they are usually thought to be more difficult 

 to grow, under some conditions yams outproduce cassava. Yams 

 fill an important role in the diet of many areas of the Tropics — a 

 role that can increase in importance. That role and its potential 

 are not, however, well understood. 



The yam is not a single species. Perhaps 60 species have edible 

 tubers; of these about 10 species can be considered crop plants. The 

 literature concerning these species is widespread but fragmentary. 

 This is the fifth of several Agriculture Handbooks in which the 

 major species of yams are individually treated in order to bring 

 the investigator as well as the agriculturist up to date with respect 

 to the status of these important plants. This is part of a research 

 effort cosponsored by the U.S. Department of Agriculture and 

 the Agency for International Development to introduce, evaluate, 

 and distribute better yam varieties. 



Also in "Tropical Yams and Their Potential" series — 



Part 1. Dioscorea esculenta. USD A Agriculture Handbook 

 No. 457. 



Part 2. Dioscorea hulbifera. USDA Agriculture Handbook 

 No. 466. 



Part 3. Dioscorea alata. USDA Agriculture Handbook 

 No. 495. 



Part 4. Dioscorea rotundata and Dioscorea cayenensis. USDA 

 Agriculture Handbook No. 502. 



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