PREFACE 



The feeding of future generations requires a knowledge of the indi- 

 vidual crop plants of the world and their potentials. Crops can be rec- 

 ommended for particular regions only on the basis of potential yields, 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 information 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 rela- 

 tively 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 last of several Agriculture Handbooks in which the major spe- 

 cies 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 

 Science and Education Administration of the U.S. Department of Agri- 

 culture 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. USDA Agriculture Handbook No. 457. 

 Part 2. Dioscorea bulbifera. USDA Agriculture Handbook No. 466. 

 Part 3. Dioscorea alata. USDA Agriculture Handbook No. 495. 

 Part 4. Dioscorea rotundata and D. cayenensis. USDA Agriculture 



Handbook No. 502. 

 Part 5. Dio scorea trifida. USDA Agriculture Hand book No. 522. 



For sale by the Superintendent of Documents, U.S. Government Printing Office 

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