THE HEVEA RUBBER TREE IN THE AMAZON VALLEY 57 
Other parasites will likely pass from the jungle to the plantations 
and become established there, but it is doubtful whether these are 
more to be feared than similar organisms which may from time to 
time transfer themselves from their jungle hosts in Sumatra and the 
Federated Malay States to the plantations there. 
Mistletoes of various types are extremely common on rubber trees 
in South America. These have been discussed by Doctor Weir, but 
it may be added here that they are as prevalent in the Purus and 
Acre Valleys as in the region of the Madeira and its tributaries and 
along the lower Amazon. Mistletoes are very common on jungle 
trees in the Orient; but, so far as the writer's observations go, they 
very rarely attack plantation rubber trees. It may be anticipated 
that they would be somewhat more troublesome on South American 
plantations, but it is doubtful whether they would become a serious 
menace. 
The brown-bast disease, which is so serious a problem on eastern 
plantations, occurs also in the Amazon Valley. The writer in com- 
pany with Doctor Weir found a tree in the jungle at Utinga, near 
Para, which showed definite symptoms of this disease. Later Doctor 
Weir located others, as he relates in his report. In the Acre Terri- 
tory the writer located a number of trees affected with this ailment. 
Numerous dead trees in this locality gave evidence of having been 
attacked by the disease, though it was impossible to be certain of 
this or of the immediate cause of their death. All the cases noted 
were of trees which were being tapped very severely. The presence 
of the brown-bast disease in South America lends weight to the 
theory that it has a physiological origin. 
As a matter of interest, rather than one of economic importance, 
the writer looked for injuries by lightning, such as have been noted 
by Rutgers (35) and himself (2.0, but no unquestionable cases were 
found. 
The South American leaf disease has been made the subject of a 
recent bulletin by R. D. Rands (84). It was very carefully studied 
also by Doctor Weir, who found it prevalent in the areas which he 
visited. It is equally prevalent along the Purus River and in the 
Acre Territories of both Brazil and Bolivia. Whether the special 
conditions which have made it so serious a detriment to rubber 
production in the Guianas will also be found in the Amazon Valley 
is not known. In any event its presence must be reckoned with, and 
any serious plan of plantation development must contemplate the 
thorough study of methods of control of this disease. 
OTHER TREES WHICH BEAR RUBBER OR SIMILAR SUBSTANCES 
Beside the various species of Hevea, there are a number of other 
rubber-bearing plants which have been exploited at one time or 
another. The most important of these, and the only ones from which 
rubber is now obtained, are species of Castilla and of Sapium. Gutta- 
percha and balata are also obtained from various South American 
trees. 
CASTILLA 
Second to the superior species of Hevea, but certainly superior in 
quality to the rubber from several species of Hevea, comes that 
from trees of the genus Castilla. This is known everywhere in the 
