RUBBER (HEVEA; DISEASES 6 
the existing dangers from plant diseases, considerable advance in 
several regions is being made. 
The studies in the Amazon Valley show in no small way the eco- 
nomic importance of the factor of disease in relation to the more 
permanent crops and the revenue therefrom. Compared with the 
work that has been done in relation to the protection of field and 
forest crops in many parts of tropical America, practical work on 
the fungous diseases of important crop plants in the Amazon Valley 
has been entirely neglected, largely because of the inactivity of 
the people and the popular belief that the native plant products are 
inexhaustible and may be exploited in any manner that one with the 
necessary capital sees fit. Consideration of future economy by con- 
servative methods of tapping and general care of trees, with a view 
to the promotion of future yields on the same site, is not a part of 
the plan for collecting rubber by the present owners of estradas. 
The rubber operator literally slashes right and left, and when the 
trees no longer respond to the methods employed he moves to un- 
worked areas. This treatment of the more accessible trees has re- 
sulted in enormous damage, so that a large percentage of the wild 
rubber growth near the streams is in a condition no longer suitable 
for tapping. It is unlikely that many of these trees can be brought 
back to a proper state of health under a well-regulated forest work- 
ing plan. After the more inaccessible areas are worked, the growing 
of rubber in plantations must of necessity be undertaken. Since the 
conditions in the Amazon Valley are suitable for growing enough 
rubber to supply the world, provided proper measures are taken to 
protect the crop against diseases, this will necessarily be the next step. 
DISEASES OF HEVEA 
Hevea in the Amazon Valley is attacked by a number of fungous 
diseases. This expression refers not only to certain wood-destroying 
and parasitic fungi acting on the root and stem, but includes a num- 
ber of leaf parasites. This means reduced vigor, rapid death, or 
slow starvation if the attack is continuous. In some section's mistle- 
toe adds its suppressing effects, and its cankers and burls afford an 
entrance to the spores of wood-destroying and other fungi and 
insects. 
The planter who may contemplate the growing of rubber in the 
Amazon Valley may expect to find it nece>sary to combat the natural 
enemies of the tree. This is not alarming. It is a condition that 
must be met, as has been the case in the Orient, and is incidental to 
the successful growing of any crop anywhere. It is merely a part of 
the overhead. There is no reason to believe that the diseases of 
Hevea encountered in the Amazon Valley can not be successfully 
combated if proper precautions before and after planting are taken. 
HOST RELATIONSHIPS 
As a matter of further introduction to the more detailed discussion 
of particular problems it is interesting to note thai many of the 
more serious diseases of the timber trees did not extend their ravages 
to Hevea, but confined their work to sets of hosts in no wise related 
to Hevea. For example, one of the most serious wood-destroying 
