18 BULLETIN 27, PORTO RICO EXPERIMENT STATION. 
large areas in the inner part of the root are of a light purplish color, 
though the predominant color of the edible portion is light yellow. 
These roots usually are tough and difficult to injure, and therefore 
keep better than most other kinds. They are fibrous and hard when 
cooked and not of pleasant flavor. The air tubers, or " air potatoes," 
grow within the axils of the leaves in great numbers when conditions 
are favorable. In fact, the average number produced per vine on the 
crop at the station for 1917-18 was 17; the total weight was 3.5 
pounds. 
These air tubers vary greatly in shape, but for the most part they 
are shaped somewhat like an egg, though more elongated at the 
smaller end. Some are almost spherical. Others are flattened, re- 
sembling a wide-open fan, edged with round, smooth notches. These 
tubers are smooth, except for numerous small indentations, and the 
interior is yellow, firm, though not hard, and free from fiber. When 
cooked, the air tubers of this variety are of excellent texture and 
rank among the best yams in flavor. The keeping qualities of the 
" air potatoes " are far better than those of any other yam tested. 
Of those examined at the station, not one decaying " air potato " was 
found, although they were handled in the same manner as other 
yams, and in many cases were kept in storage for months. Their 
keeping qualities are partly due to their firm outer skin and partly to 
their size. They are smaller than most other kinds and are less likely 
to be injured at harvest time than roots that must be dug. The starch 
content of the " air potatoes " of this variety, calculated on the fresh 
sample, was 12.46 per cent, and of the edible root 17.95 per cent. 
DIOSCOREA CHONDROCARPA. 
A variety of this yam was imported from New Guinea and sent to 
the station as S. P. I. No. 31920 through the Office of Foreign 
Seed and Plant Introduction of the Bureau of Plant Industry, United 
States Department of Agriculture. It has been grown for a few 
seasons in the station's plat (PI. V, fig. 2) and has been found to be 
one of the heaviest-yielding yams. It has a high starch content, 
that for the fresh yam being 25.32 per cent. While it is not so rich 
and agreeable in flavor as some other yams, it is nevertheless recom- 
mended for trial in all parts of the island. 
The yield of this variety when planted in suitable places aver- 
aged over 5 pounds per hill, and many individual hills produced roots 
weighing twice this amount. The yams are generally flattened or 
fan-shaped and divided along the lower margin into many rounded 
lobes. The rootstock is white, large, and woody, and the upper part 
of the edible portion is somewhat tough. The hardness and yellow- 
ish color, however, gradually diminish at the center, and at the lower 
