12 BULLETIN 27, PORTO RICO EXPERIMENT STATION. 
this bulletin were under cultivation at the experiment station at 
Mayaguez and do not include all the large number of varieties known 
in Porto Rico. (PL I, fig. 1.) 
GUINEA. 
The yam localty known as Guinea is a variety of the species 
Dioscorea sativa, and is one of the most popular yams in Porto Rico. 
It is widely distributed over the island, upland clay soils to which 
it is best suited being accessible to almost every family. Its pro- 
duction is probably greater than the combined yield of all other 
varieties grown in the island. In the city markets it retails usually 
at a somewhat higher price than any other kind except the variety 
known as the Mapuey morado. The vine grows quickly and ma- 
tures earlier in the fall than any of the other varieties under dis- 
cussion. The roots, though generally cylindrical in shape, are occa- 
sionally divided into two, three, or even four parts at the lower 
end (PL I, fig. 2). In a normal plant the root should measure about 
4 inches in diameter, 12 or 14 inches in length, and weigh about 6 
pounds. The outer covering of the root is thick, rough, and corky, 
and the edible part is pure white. The texture is uniform throughout, 
fine-grained, brittle, easily bruised, and free from fiber. The starch 
content of normal roots, as determined by the chemical department 
of this station, is 24 per cent of the fresh root. When cooked it is 
firm, tender, and granular, retains sufficient moisture to be palatable, 
and has a rich, sweet, and altogether pleasant flavor. For table 
use it ranks among the best. 
Any part of the root may be used if planted at a time when the 
moisture is sufficient but not excessive. However, the top part of the 
yam yielded considerably more than the other parts when planted at 
the station. The yield from plantings of middle or lower sections 
was about equal. The maximum size of cuttings for plantings seems 
to be about three-fourths pound, owing to the fact that larger pieces 
are frequently attacked by decay after they are planted. This is 
true more especially when the roots have been injured or subjected 
to unfavorable weather. Large top sections are preferable to large 
center sections when yams are desired for market. The roots pro- 
duced by the former, though fewer in number, are much larger and 
therefore always sell more readily than those produced by the 
latter. When roots are desired for planting the following year, 
center sections weighing about three-fourths pound should be pre- 
ferred over top pieces or crowns. A number of yams develop along 
the margin of the cut area of these sections and these in turn develop 
into small or medium-sized roots. The formation of three to seven 
yams on one seed piece greatly increases the number of crowns for 
