Edible Products. 



32 



(July, 1912. 



YAMS. 



By O. W. Barrett, 

 Chief, Division of Experiment Station. 



(From the Philippine Agricultural Re- 

 view, Vol. V., No. 2. February, 1912,) 



It would be fairly easy to name the 

 five most important food plants of the 

 world but the second five would be a 

 much more difficult matter to decide 

 upon. The true place of the yams in the 

 world's list of economic plants is a debat- 

 able matter, but for the sake of argu- 

 ment we may regard them as holding 

 about fifth place. It must be remem bered 

 in this connection that outside of Europe 

 and North America nearly all the inhabi- 

 tants of the earth's surface are either in 

 China or in the Tropics, and while China 

 makes use Of but oi^e or two varieties of 

 yams, both the Old and the New World 

 Tropics depend to a very large extent 

 upon this root-crop as a food supply 

 throughout the greater part of the year. 



On account of the habit of the plant 

 itself, the methods of culture, storage, 

 and sale, yams are not prominently in 

 evidence and consequently many travel- 

 ers, and even residents in countries like 

 India or the West Indies, do not apprec- 

 iate, and in many cases it seems, do not 

 even know the important role of this 

 crop. For instance in Porto Rico, where 

 yams rank as the second most important 

 root-crop, they are seldom used by the 

 American families unless the family in 

 question has resided there for several 

 years ; in fact, it is a common case for 

 the housewife to purchase third-class and 

 almost inedible potatoes at from 30 to 40 

 centavos a kilo, when close by the side 

 of the potatoes there are heaps of excell- 

 ent yams, offered at about 10 centavos a 

 kilo. Probably the rough, coarse appear- 

 ance of yams accounts, in part, for this 

 lack of popular favor which is so evident 

 among European and American residen ts 

 in the Tropics. 



It is certain, however, that the yam is 

 one of the very oldest cultivated root- 

 crops, having been grown in India for 

 many centuries ; it was also an import- 

 ant crop of the aborigines of Tropical 

 America when the early Spanish navi- 

 gators entered that region. In fact, 

 it would seem that yams vie with the 

 sweet potato, the taro, and the yautia 

 for antiquity in point of cultivation by 

 man,— all these food plants having been 

 under domestication so long that they 

 seldom or never produce seeds. Some 

 species of yams do, however, on very 

 rare occasions produce flower clusters 

 and a few of the domesticated species 

 undoubtedly produce viable seeds under 

 favourable conditions. The yams have 

 broken the regulations, so to speak, for 

 plant reproduction in two ways : A 

 number of varieties commonly produce 

 small, or in the case of the air-potato, 

 large tubers in the axils of the leaves 

 (a rather rare infraction of the law); 

 further more they all (?) possess the 

 trait of sending out sprouts from almost 

 any part of the surface of the tuber-like 

 root which, however, is not very uncom- 

 mon in the plant world. 



Botanically the yam family is rather 

 closely related to the smilax and the lily 

 families, yet for certain reasons it stands 

 alone in a class by itself. There are 

 supposed to be only aboat 160 speciea 

 in the family, which consist* of some 

 eight or nine distinct genera, but prac- 

 tically the entire family depends upon 

 the genus Dioscorea which comprises 

 about 150 botanical species. Of these 

 150, only some ten or twelve species are 

 important in the world's food supply list 

 and probably three-fourths of the culti- 

 vated varieties are included under not 

 more than five or six species ; however 

 the actual number of distinct varieties 

 and named sorts comprised under these 

 few species is unknown. For some reason 

 both the economic and the taxonomic 

 botanists have neglected this most in- 

 teresting group of plants ; specimen 

 sheets showing only leaves are not desired 

 by the herbarium student and it appears 

 that no collection which could in any 

 way boast of being fairly complete has 



