40 BULLETIN 1380, U. S. DEPARTMENT OF AGRICULTURE 
Any plan of direct eradication would require the cooperation of 
neighboring estates and a consideration of cost. 
IMMUNIZATION 
Very rarely individual trees standing among infected groves are 
entirely free from the disease. Whether such trees have developed 
immunity or are uninfected through accident of spore distribution 
it is impossible to state. Harrison calls attention to the fact that 
in every plantation healthy trees are observed. However, individ- 
uals showing resistance and other desirable qualities could be se- 
lected for experimental work on the chance that immunization may 
come from certain individual peculiarities and can be stabilized. 
Since the trees may be propagated by means of cuttings and 
grafts, results could be obtained in a comparatively short time. 
Bancroft in explaining the ravages of the fungus in plantations has 
suggested that Hevea of an especially susceptible type may have been 
selected in the beginning. It is interesting to recall that practically 
all plantations were started from stock obtained in the lower Ama- 
zon Valley, where the ravages of the disease were observed to be 
most severe. Likewise, the seeds originally taken from Brazil by 
Wickham may have been chiefly from the white variety (branca) of 
Hevea, which, so far as observations have been carried, appears to be 
very susceptible to the disease. 
It is not known whether Hevea will cross with other related rub- 
ber-producing trees. The latter are not attacked by the disease. 
Rorer is of the opinion that the only hope of combating the disease 
is through the development of resistant types. Rands, in his work on 
brown bast, has demonstrated the practicability of creating resistant 
strains. It appears, however, tluit much may be learned by thor- 
oughly investigating the influence of environmental factors on the 
development of the fungus. 
THE DISEASE IX THE FOREST 
Although the disease as shown is widely distributed in the Amazon 
drainage, it is only in the lower stretches of the valley that the 
disease was observed to be very destructive. At many of the points 
visited along the Madeira River and at points farther on in Matto 
Grosso, trees of any age class and with leaves in all stages of de- 
velopment on terra firma were either free from the disease or but 
slightly influenced by it. Very few infections w T ere observed at 
Manaos. 
On the Rio Beni in Bolivia the disease was scarcely noticeable at 
the several stations visited. The magnificent size and quality of the 
trees in the upper Amazon drainage on terra firma would seem to 
imply that the disease has had but little influence on their develop- 
ment. 
It is the writer's opinion that when a thorough survey has been 
made of the available territory, regions will be found where Hevea 
may be grown without much danger of the profits being reduced 
by the action of this disease. There is no reason to believe that 
Hevea undergoes a change making it more susceptible to the disease 
when grown under plantation conditions. It should be remembered 
