Vegetables with Edible Tubers or Roots 263 



But in tropical countries, where the Irish potato can only 

 be raised on the mountains, or during the cool season, the 

 best kind of yams should find a place in the vegetable 

 garden. Several varieties of yam have the advantage over 

 the sweet potato as a staple food in that they can be kept 

 for a much longer period out of ground without damage. 

 Yams are also easy to grow, and may be planted at all 

 seasons of the year and taken up from the ground almost 

 at any time when they are wanted, so that a constant 

 supply may be had. They form the staff of life of the 

 negro population of the Antilles. 



The yams are propagated by cutting off the top of 

 the rootstock and planting it again with the attached 

 vines ; or after this has grown for a few months, the yam 

 it produces is cut up into pieces with buds on each, and 

 these pieces used for a new crop ; or the top of the yam 

 may be cut at once into "sets." The "sets" are planted 

 several in a hill with a stake to climb on, at 6 to 8 feet 

 apart, or are allowed to trail on the ground. They have 

 been found to give better returns when staked. The 

 yams are ready in seven to eleven months. Several 

 yams may be produced by one plant, and according to the 

 species or variety may weigh from a few ounces to a 

 hundred pounds each. The produce may be a dozen 

 tons to the acre. 



The white or square-stemmed yam is the most exten- 

 sively grown, and there are many varieties of it, some with 

 purple flesh. 



The small yam from South America, called cushcush, 

 with three-lobed leaves, is one of the best to use as a table 

 vegetable. There are a hundred or more other species 



