LEAF DISEASE OF PAR A RUBBER 15 
leaf at a different time or to other factors. Nevertheless, the chances 
seem promising enough to warrant the attempt, and this should not 
be delayed, because many of the deserted plantings are gradually 
being cut down and replaced by other crops. 
Until resistant strains are isolated or until further study has 
demonstrated a practicable method for preventing or controlling the 
leaf disease, the establishment of new plantings in the Guianas is 
not likely to be attempted. Although favorable localities in these 
regions might be selected, the disease will nevertheless be a latent 
menace to the enterprise. 
EXCLUSION FROM NONINFECTED REGIONS BY QUARANTINE 
Although at present it is scarcely advisable to plant Hevea in in- 
fected regions, there are doubtless extensive areas in other parts of 
the western Tropics equally suited to its culture. It is important, 
however, that these uninfected countries prevent the possible intro- 
duction of the disease by establishing suitable restrictions on the 
importation of propagating material. The general efficacy of quaran- 
tine measures has been sufficiently demonstrated with respect to 
other diseases not to require elaboration here. Since further natural 
spread of the disease is limited by sea and mountain barriers (see 
fig. 1), it is unlikely to reach other regions except through ocean 
commerce. Importations from the infected countries should be al- 
lowed, therefore, only under Government supervision and limited 
to seed and large " stumps," which do not carry the disease, 
SUMMARY 
The discouraging outcome of the formerly very promising rubber- 
plantation industry of the Guianas has been recognized for some 
time to have been largely due to the ravages of an endemic leaf dis- 
ease which spread from the scattered wild trees of the jungle 
to the closely spaced plantings. In consequence of recent agitation 
for a near-by source of crude rubber, attention is again focused on 
the American Tropics and has naturally raised the question as to 
what extent this leaf disease will be a factor in contemplated enter- 
prises. Since the trouble has been studied considerably in the past 
fry local botanists, this bulletin presents mainly a review of the pres- 
ent situation obtained during a visit to the infected regions, a sum- 
mary of the main facts known about the disease, and suggestions for 
future procedure. 
The disease occurs apparently throughout the indigenous range 
of the genus Hevea, which includes Peru, Brazil, and the Guianas. 
It is also established on the island of Trinidad, having probably been 
imported along with propagating material. 
The South American leaf disease is doubtless the most serious 
trouble which affects its cultivated host (Hevea tra-siliensis) . 
Through its injury to the foliage it not only makes tapping unre- 
munerative but under favorable conditions repeated defoliations 
result in extensive die-back of the branches and actual death of 
large numbers of trees. 
The amount of damage to the industry from the leaf disease in 
Trinidad has been much less than in the Guianas, owing probably 
