Among the minor species, a few can be distinguished as more impor- 

 tant than others. But because this distinction is among types that may 

 not differ significantly, there is no exact point on which the minor species 

 mentioned in this handbook can be distinguished from those not men- 

 tioned. The authors consider the following species to be more important 

 than other minor species listed in table 1: D. dumetorum (Kunth) Pax, 

 D. hispida Dennst., D. pentaphylla L., D. nummularia Lam., and D. 

 transversa R. Brown. All these species are cultivated for food, although 

 probably all have wild races or uncultivated counterparts. All have been 

 introduced from their geographical origins to other regions. All but the 

 last are fairly well known to plant scientists and are available, although 

 perhaps with difficulty. These generalizations are not true for most of 

 the other minor tropical species listed in table 1. All are little known with 

 respect to their potentials as crop plants. 



Few other generalities can be made, for these five species represent 

 a mixed group. They come from two continents, some are poisonous, and 

 they differ widely in morphology. These yams merit further study in 

 their areas of origin and wider introduction so that their potentials can 

 be tried. Recently, the almost unknown species D. transversa was in- 

 troduced as a cultivar, 'Wael', to the French West Indies, where it has 

 been highly successful. Study of the minor species will surely reveal 

 varieties of potential for different parts of the Tropics. These minor 

 yams also merit more treatment in the literature, for reliable informa- 

 tion concerning them is difficult to obtain. 



Domestication and Distribution of Minor Species 



The five minor species of yams considered here have been only 

 partially domesticated. Of these, the most primitive is D. hispida, which 

 is seldom cultivated but is frequently sought from the wild, especially 

 as a famine food. Its tubers are often near the surface of the soil, making 

 it an easily obtained food, and this availability may compensate some- 

 what for the great difficulties of ridding it of poison. 



On the other hand, the wide distribution of three other species 

 suggests the active intervention of people. In carrying tubers from place 

 to place, people have valued and taken care of them. Apparently, D. 

 transversa is still limited in its distribution. 



The domestication of Z). dumetorum must have been related to that 

 of D. rotu7idata (L.) Poir. and D. cayenensis Lam. , the principal African 

 yams. Chevalier (7) observed a kind of D. dumetormn protoculture in 

 which wild yams were gathered for food and the extras planted. Within 

 the tradition of a yam-based culture, the edible qualities of all species 

 were probably tested. D. dmnetorum has achieved a status between the 

 domesticated species and the wild species {D. preussii Pax, D. lieb- 

 rechtsiayia de Wild., D. minutiflora Engl., and other species). 



The events in the domestication of D. pentaphylla are difficult to 



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