YAM CULTURE IX PORTO RICO. 13 
future planting. One-half pound seed pieces develop fewer roots, 
and seed pieces weighing one-fourth pound or less seldom yield 
more than one yam per hill. 
POTATO. 
A small rooted variety (PL II, fig. 1) resembling an Irish potato 
and introduced from Africa a few years ago has been distributed to 
many parts of the island. This variety is known in Porto Rico as 
the Potato yam. In some places it is considered among the best 
for home planting, and in a few of the city markets of Porto Rico it 
is bringing good prices. The Potato yam should be planted in all 
parts of the island except where the soil is light and sandy. It will 
not thrive in such soil. 
The vines of the variety are slender, round, of moderate growth, 
and remain green later in the dry season of winter than any other 
kind, except the variety known as Congo, the vines of which grow 
throughout the year. A dozen or more short, strong, sharp spines 
develop between the nodes of older parts of the vine. The leaf petiole 
is round and slender, has a few spines resembling those on the vine, 
and at its base has two long sharp spines. The leaves appear alter- 
nately. The edible roots develop near the crown of the plant much 
the same as sweet potatoes. They are oval and vary up to 8 inches in 
length, and 2J inches in diameter. As they are small and not easily 
injured, these roots can usually be kept longer after being harvested 
than the large-rooted kinds. They are smooth, dark grayish-brown, 
and at a distance of a few feet are likely to be mistaken for the Irish 
potato. The skin is very thin and tough, and may, after being broken, 
be pulled off in strips resembling thin pieces of cherry bark. The 
interior of the root is over 23 per cent starch. It is white, brittle, and 
firm, and practically free from fiber when not allowed to remain too 
long in the soil. However, roots which are left in the soil until late 
in the winter sometimes have a few long and rather strong, longi- 
tudinal fibers. When cooked the roots are fine-grained, tender, and 
sweeter in flavor than most other varieties. 
Since the small yams develop in the surface soil and are not hin- 
dered by a compact subsoil, the Potato variety thrives best in rich 
soil and better than most other varieties in heaw clays. This variety 
yields poorly in sandy soil, and produces angular or flattened tubers 
in heavy, compact soil. The land selected for planting should be 
kept free from weeds and grass, so that cultivation will be unneces- 
sary during the first five or six weeks of the plant's life. 
The table following shows the results of tests made to determine 
the effect of planting large and small roots of the Potato variety at 
different distances, as well as the result in yield of planting on level 
land and on ridges. The tests were made with roots slightly above 
