CULTIVATION OF THE TRUE YAMS. 3 
except for a more or less bitter taste. It is very popular among the 
West Indians. In Porto Rico it is also known as the Congo or 
Congo amarillo, and in Jamaica as the yellow, or affou, yam. The 
tubers (PL III, Fig. 1) often reach a weight of several pounds each. 
They do not keep very well. The vine is round, glossy dark green, 
and thorny, with alternate leaves. In the Tropics this species re- 
quires about 12 months to mature. 
The lesser yam {Dioscorea esculenta (Lour.) Burkill), including 
many varieties, usually produces rather small oval tubers (many in 
a hill), weighing from less than a pound to nearly 2 pounds each. 
They generally keep well. The skin is thin, tough, and usually 
smooth (PL II, Fig. 1), and in some varieties the tubers are covered 
with hairy roots. The plants have underground thorny stems near 
the surface of the soil which, though they increase the difficulty of 
harvesting the crop, also serve to protect the tubers from the depre- 
dations of animals. 
In general, the lesser yam requires a rich, loamy soil. Snowy 
whiteness and more or less sweetness of the flesh when cooked charac- 
terize the best varieties. The flesh is very mealy, though in some 
varieties there is at times considerable fiber. The vine is round and 
bears a variable number of short spines between the leaves, with a 
pair of somewhat longer ones at each leaf. The leaves are broadly 
heart-shaped and alternate. 
The acorn {Dioscorea latifolia Benth.) bears its crop of tubers 
aboveground in the axils of the leaves. These aerial tubers (PL II, 
Fig. 2) are angular and have a greenish gray skin; the largest reach 
a weight of nearly a pound. The flesh is dull yellow and rather dry ; 
when cooked it is very firm and of fair flavor. Acorn tubers are 
remarkable for their keeping qualities. The vine is round and spine- 
less, and the leaves are broadly heart-shaped and alternate. Various 
local names, having such meanings as " turkey-liver yam," " climbing 
air potato," and " Carib potato," are in use in different parts of 
tropical America. , 
The white Guinea yam (Dioscorea rotundata Poir.) 5 is grown in 
Porto Rico under the name of Guinea yam (PL IV, Fig. 1). In 
) Jamaica and some other localities it is known as the negro yam. It 
is white fleshed and is one of the best and most popular yams culti- 
vated in the West Indies. In Porto Rico this yam grows best in 
clayey soils. It matures in a shorter season 6 than other yams. The 
tubers weigh up to 6 pounds each. The glaucous vine is round and 
armed on the older parts with short but strong recurved thorns. The 
leaves are opposite. Many forms 7 of this species are reported to 
exist in Africa, its native home, but only one appears to be known in 
the West Indies. 
The yampi (Dioscorea trifida L. f.) exists in several distinct vari- 
eties. The Jamaica yampi (PL III, Fig. 2) is one of the best known. 
1 A variety grown in Trinidad is known locally as cush-cush. The 
tubers of the different types of yampi vary in size, form, and color 
5 Burkill, I. H. The correct botanic names for the white and the yellow Guinea yams. 
In Gardens* Bui. Straits Settlements, v. 2. p. 4.38. 1921. 
9 Kinman, C. F. Yam culture in Forto Rico. Torto Rico Acr. Exp. Sta. Bui. 27, p. 12. 
1921. 
7 Burkill, I. H. Some cultivated vams from Africa and elsewhere. In Gardens' Bui. 
Straits Settlement, v. 2, p. 87. 1918. 
