22 BULLETIN 27, PORTO RICO EXPERIMENT STATION. 
Either entire or parts of roots may be planted, although the crown 
or upper section was found to give the most satisfaction at the experi- 
ment station. Dipping in Bordeaux mixture was found to be an 
effective means of preventing decay of roots cut in pieces for seed. 
Applications of fertilizers did not result in sufficient increase in 
the crop to warrant their recommendation. Where fertilizers are used 
none of the elements — nitrogen, phosphorus, or potash — should be 
omitted. 
Tests in pruning the vines resulted in each case in a marked de- 
crease in production. Yields were low also where supports had not 
been provided for the vines. 
In harvesting yams care should be taken to avoid bruising the 
roots, because injured roots are usually attacked by disease and then 
decay. 
Among the varieties commonly grown in Porto Rico, the one known 
as Guinea is the most desirable on account of its heavy yield, 
its high food value, and its pleasant flavor. The variety called 
Mapuey morado sells at a higher price than other yams, but its yield 
is usually low. 
Among the lately introduced varieties recommended for general 
planting, the one known as Potato, which was introduced from 
Africa, and a variety of the species Dioscorea alata from New 
Guinea, produce heavy crops of roots having a high food value and 
palatable flavor. 
o 
