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 use in particular regions only on 

 the basis of potential yield, the costs of production, the food and 

 feed value of the crop, and the way the crop can be processsed or 

 otherwise used. For most of the major food crops of the world, 

 a body of information is already 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 while 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 frag- 

 mentary. This is the fourth of several Agriculture Handbooks in 

 which the major species of yams are individually treated in order 

 to bring the investigator as well as the agriculturalist up to date 

 with respect to the status of these important plants. This is part 

 of a research effort cosponsored by the Agricultural Research 

 Service of 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 bulhifem. USDA Agriculture 



Handbook No. 466. 

 Part 3. Dioscorea alata. USDA Agriculture 



Handbook No. 495. 



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