THE HEVEA RUBBER TREE IN THE AMAZON VALLEY 65 
BALATA 
A considerable quantity of balata, a substance extensively used 
for special purposes, such as the manufacture of belting, is extracted 
from jungle trees in the Amazon Valley. Most of this comes from 
the valley of the Rio Negro, which the writer was unable to visit. 
Therefore, no first-hand information can be given here. Balata is 
obtained entirely from wild trees (species of Mimusops) growing in 
the jungle. Promising species of balata trees should be tested in 
cultivation. 
NEED OF INTRODUCTION OF OTHER SPECIES OF HEVEA 
It may seem to man}^ that so long as we have a rubber tree as good 
as the one now in cultivation, there is no need to seek further for other 
types of trees. The tree now grown on the plantations gives a product 
satisfactory both as to quantity and quality. However, planters 
believe in the possibility of increasing both the yield and the quality 
of the rubber, and selection experiments are being carried on with 
the hope of considerable improvement in plantation strains. 
It is well known to plant breeders that selection creates nothing 
new but merely picks out and isolates desirable qualities which 
appear in the material under study. Therefore, there is a decided 
limit to the improvement which can be brought about by selection. 
The introduction of new strains frequently gives material for selec- 
tion superior to anything formerly cultivated. An example of this 
is found in Cinchona, the tree from winch quinine is derived. All the 
cultivated species of Cinchona were introduced to India and Java 
from South America, where they grew on the eastern slopes of the 
Andes Mountains. The climate of Java proved most satisfactory 
for the growth of the tree, and that country became the chief center 
of Cinchona cultivation. 
As the industry developed, attention was paid to the improvement 
of the strains in cultivation. Selection resulted in increased yields, 
but plant exploration and introduction were begun also. In Cinchona 
ledgeriana a species was found which greatly excelled any plant pro- 
duced by selection and revolutionized the production of quinine, 
resulting in making this indispensable drug generally available at a 
low price. 
The possibility of the introduction of the South American leaf 
disease into the Orient may be remote, but it does exist. From the 
nature of the disease, the use of resistant varieties seems to offer the 
best means of control. According to Rands (34), varying degrees of 
resistance are shown by the trees in infected districts in the Guianas. 
It may be impossible to find resistant individuals which also have a 
very high yielding capacity, but there is a possibility of combining 
the two qualities by the crossing of strains. 
There is a constant tendency for new diseases to appear, either 
through introduction from other places or through the adaptation of 
some local organism to the plant as a host. Some of these diseases 
can be combated effectually only by the use of resistant strains. 
Comparatively few of the many known species of Hevea are now in 
cultivation. It may be that some of the little-known species may 
supply the basis for breeding a strain resistant to some very dangerous 
96522°— 26 5 
