20 BULLETIN 27, PORTO RICO EXPERIMENT STATION. 
kinds, and 50 per cent below that of the varieties giving the highest 
starch content. 
A variety of D. dlata (PI. VI, fig. 1) from New Guinea, was lately 
introduced through the Bureau of Plant Industry, United States 
Department of Agriculture, as S. P. I. No. 31919, and seems to be 
well adapted to conditions in Porto Rico. The roots are slender and 
very long, and, as a result, they can not, except with difficulty, be 
harvested without injuring them. The variety does not withstand 
drought as well as some other varieties and its yield is slight, a pro- 
duction of 3 pounds per hill being exceptional. For these reasons, 
this yam can not be recommended for general planting. The roots 
are thick-skinned and rough. The interior is somewhat coarser 
than that of most other varieties, has a tinge of brown, and like most 
water yams is fresh in appearance. When cooked it has little sweet- 
ness and lacks richness of flavor. 
Another yam, said by P. J. Wester to be a D. cdata variety, and in- 
troduced from New Guinea under S. P. I. No. 34861, has shown it- 
self especially well adapted to the heavy clay soils of Porto Rico. 
It possesses a richer and more pleasing flavor than the D. alata 
variety above mentioned. Its roots have a diameter of 2J to 3-J 
inches, and are very long, sometimes attaining a length of 3J feet 
in one season (PI. VI, fig. 2). The edible roots do not grow per- 
pendicularly but at an angle, and often almost horizontally along the 
bank. Inasmuch as the roots can not pierce hard earth, the banks 
should be large and well-prepared, so that a well-shaped product 
will be insured. Otherwise, the roots on reaching the bottom of the 
bank will be deflected. Sometimes they turn at a right angle or in 
such a manner as to form a complete circle when the point reaches the 
top of the bank. On account of these peculiarities of growth, this 
variety is difficult to dig without injury to the roots. 
DIOSCOREA CAYENNENSIS. 
A variety of this species is grown in many parts of the island and 
is well known in some localities. In Mayaguez it is called " Congo 
amarillo," but in the San Juan market, where it is found in greater 
abundance than other kinds, it is known as "Yellow Guinea." It 
thrives much better in sandy soils than most yams, and is therefore 
preferred in some sections. The edible root of this variety closely 
resembles the " "White Guinea " in shape and size, though the 
skin is thick and somewhat more corky than the latter. The large 
roots attain a length of probably a foot, are rather cylindrical, and 
average a weight of 4 or 5 pounds in seasons when weather condi- 
tions are favorable. The interior of the starchy root is a rich light 
yellow and turns dark brown when exposed to the air. It is smoother 
