PREFACE 



The feeding of future generations requires a knowledge 

 of the individual crop plants of the world and their poten- 

 tials. 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 processed 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 wide- 

 ly 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 wide- 

 spread but fragmentary. This is the third of several Agricul- 

 ture 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 U.S. Agency for 

 International Development to introduce, evaluate, and dis- 

 tribute better yam varieties. 



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