RUBBER (HEVEA) DISEASES 21 
As a saprophyte it occurred on a great variety of substrata. Dead 
stems of Hevea thrown in moist places were found to be covered 
with the fructifications of the fungus. It was especially common 
on dead stems of the witches'-broom on cacao. On the immature 
fruit of cacao the fungus was invariably present, covering the entire 
surface with a dark-brown or black sooty layer. Immature Hevea 
pods gathered one day and rolled up in oiled bags would be covered 
with the fungus three days later. The fact that the fungus as a rule 
enters the host only by way of injured branches and that it rarely 
takes advantage of the mutilation of the tree in tapping as at present 
practiced indicates a tendency to confine its activities to those parts 
of more recent development. On tapping wounds the fungus was 
first observed on the dead cortex around the cut, but had not invaded 
the living tissues or stained the wood. In later discovered cases 
the fungus exhibited a greater degree of parasitism, the affected 
area extending below the cuts for several centimeters. The dark- 
colored mycelium was present in the wood, forming narrow dark 
parallel lines similar to those commonly called " black thread " and 
referred to Phytophthora as the causal agent. 
La Rue and Bartlett have obtained results from inoculations with 
Dipiodia which have led them to state that infections in the wood 
produce black streaks and that they are not distinguishable from 
the black-thread disease usually attributed to Phytophthora. In 
the latter the dark lines as a rule are due to the infiltration of the 
wood with substances from the seat of infection and do not contain 
mycelia. 
Dipiodia was first observed on Hevea as a saprophyte on pruned 
branches on living trunks injured by fire, on fruits of the previous 
year killed by Phytophthora and still hanging to the tree, on stubs of 
improperly pruned branches (where it apparently acted as a wound 
fungus), and on twigs that were being weakened or killed by re- 
peated defoliation or infection by Dothidella ulei. The last condi- 
tion in the vicinity of Para seems to be the initial cause for the 
attack of the fungus on Hevea. Other fungi, however, were occa- 
sionally found associated with it. (See " Fungi reported on 
Hevea," p. 83.) 
The general aspect of infected trees is the presence of dead termi- 
nal twigs. One such tree, about 10 feet high, in the edge of the 
jungle near a small plantation in the vicinity of Para was carefully 
examined. Ten different twigs were dead, and the disease had 
extended downward to the first lateral branches, which in turn were 
either dead or in a languishing condition. The wood of the in- 
fected stems was blackened by the reflected color of the dark-gray 
or brown mycelium, after the manner of Ceratostomella species in 
the sapwood of timber trees. Examination of the wood ahead of the 
blackened areas shows the mycelium to have extended beyond the 
zone of evident infection from 1 to 4 inches and to be colorless. For 
this reason, as Petch has pointed out, discolored wood does not 
indicate the most forward region invaded bv the fungus. The 
bark on the infected branches dries and cracks, exposing a dark 
film on the surface of the wood. 
In the case of infection on a pruned stub 2 inches in diameter pro- 
jecting some 4 inches, it was observed that the fungus had progressed 
