YAM CULTURE IX PORTO RICO. 15 
■od and the soil loosened to a good depth, or on low ridges As a 
consequence, the land is prepared more quickly and at 1 :pense 
than where large ridges are required. 
TONGO. 
This variety (PL IV. fig. 2) was sent to the Porto B xperi- 
ment station in 1915 from Xew Guinea through the Bureau of PL 
Industry, United States Department of Agriculture. It was known 
as S. P. I. Na 31923. and was identified by P. J. Wester - as L> 
'/.leata, locally known as the Tongo. It has proved so satisfactory 
that it deserves recommendation as a very promising yam for Porto 
Rico. The plant so closely resembles the variety called Potato that 
it would not readily be distinguished bv the casual observer. How- 
ever, its leaves are somewhat larger and slightly different in form. 
The folia ore of both is lip;ht erreen and does not become dry until late 
in the dry season. Neither of these varieties produces as heavy a 
vine growth as most other kinds. Each variety sends out a number 
of underground stems that are 1 to 4 feet long:. Thev art found near 
the surface of the ground. These stems are set with long, sharp 
thorns, which are a hindrance at harvest time. 
The Tongo prefers a fertile loam soil, although good crops were 
produced in rather heavy clay at the station. Since the roots of this 
variety do not grow as deep as those of some other varieties, low 
banks are sufficient to enable them to attain normal development. 
Weighings were made at the 1916 harvest to determine the relation 
of the size of the tubers produced to the size of the tubers plant 
It was found that the tubers obtained from the 235 plants grown 
from large seed tubers were on the average 17 per cent larger than 
those obtained from an equal number of plants grown from small 
-ers. The edible roots are larger than the Potato yam. but are 
small compared with the largest rooted yams. They are produced 
in hills much the same as s^~eet potatoes. The roots vary in size from 
those too small to be of value for table use to 1 hes in length and 
3 inches in diameter. They are smooth, except for numerous short 
roots that grow on them. These are grayish-brown and much more 
numerous on the upper half of the roots. The skin is very thin and 
resembles that of the Potato vara. However, it is not as tough and 
does not separate so easily from the inner part of the root as is the 
case with the Potato yam. The edible pan of the root retains its 
snowr whiteness after being" cooked, has an agreeable texture, is verv 
fine-grained, and is sweet and rich in flavor. 
Planting roots weighing about 1 ounces gave best results in test- 
at the station. Roots twice this size made a slightly greater yield. 
Those weiffhine: but 2 ounces yielded almost 40 per cent les~ than for 
'Philippine Agr. Rev.. 9 [1916 . No. 3. p. 194. 
