12 BULLETIN 1286, TJ. S. DEPARTMENT OF AGRICULTURE 
young leaves are present throughout the year. A continuous re- 
serve of viable conidia is thus maintained. 
Under the above conditions, a resistant resting stage to carry the 
fungus over unfavorable periods is hardly needed, but the impor- 
tance of such a stage in dissemination over long distances and from 
one country to another is apparent. Since Stand's infection studies 
with ascospores were few and gave only negative evidence, addi- 
tional investigation employing different methods and ages of mate- 
rial is needed to determine the part played by the perithecial stage 
of the fungus in the perpetuation of the disease. Still more impor- 
tant is a knowledge of the longevity of the mycelium in twig lesions, 
of which nothing is known. In view of the present tendency to 
propagate the tree by bud grafting, the danger of possible spread 
of leaf disease by means of hibernating mycelium in lesions on the 
budwood is evident. 
The fungus is probably never carried by the seed, because the pod 
lesions are superficial and adhering spores probabry could not infect 
the hard mature seed coat. Since the fungus is apparently unable 
to maintain an independent saprophytic existence, the chances of 
its transmission over long distances other than in lesions of plant 
parts are very slight. 
That the disease on the plantations in the Guianas originated from 
the wild Heveas is well illustrated in an instance cited by Stahel in 
1919 (&£)? of which the following is a summary : 
From 1911 to 1915 a mining company at Lawa, on the upper Marowyne 
River, put out 40,000 trees of Hevea brasillensis. Since the trees were grown 
from imported seeds and stumps and the estate was located some 200 kilometers 
distant from the nearest Para rubber planting, the chances of the disease being 
introduced were very slight. Although the estate was reported to be in a very 
healthy condition as late as 1917, collections of leaves received at Paramaribo 
showed the presence of the disease. According to the manager of the estate, 
nothing abnormal occurred until March, 1918, when as a result of heavy fog 
frequently covering several hilltops planted with rubber, the disease appeared 
in epidemic form and spread to the rest of the planting. In six months' time, 
as a result of repeated loss of the young leaves, one-third of all the trees 
died, and the remainder showed a hopeless condition. This very promising 
estate was therefore completely ruined in a half year's time and was subse- 
quently deserted. 
ENVIRONMENTAL INFLUENCES ON THE DISEASE 
BIOLOGIC FACTORS 
The establishment of pure stands of the rubber tree, which in its 
native habitat occurs scattered or in small groups amid the wild 
confusion of other jungle species, is apparently the major reason for 
the great damage from the leaf disease. Unfortunately, very little is 
known about the behavior of the disease in the jungle, although 
Kuyper (13) found it generally prevalent on the wild Hevea guyan- 
ensis. It seems reasonable to suppose that after long association in 
their native habitat the relations between parasite and host have 
reached a state of equilibrium which becomes unbalanced upon the 
establishment of the latter in pure stands. The greater proximity of 
the planted trees combined with their natural variability in leaf 
renewal favors directly the epidemic spread of the fungus. The pos- 
sibility, suggested by Belgrave (4), that in its altered environment 
