162 
F. T. Brooks. 
same period, hence the effect upon the inoculated tissues was not 
due to the entrance of other micro-organisms from the soil. The 
absence of infection in the uninjured roots of these four-year-old 
trees is certainly striking, although as described above, the fungus 
succeeded in invading the uninjured surface of the root of one of 
the seedling plants. 
Treatment. 
It has already been pointed out that in Malaya this disease 
chiefly affects old rubber trees. It is likely that the death of old 
plantation trees has often been attributed to Fomes semitostus 
(Fomes lignosus) when the loss was really caused by Ustulina 
zonata or by Splicer ostilbe repens which also attacks mature trees 
more frequently than young ones. Fomes semitostus (Fomes 
lignosus) does not often attack old rubber trees partly because by 
the time a plantation is ten years old this fungus has generally 
worked itself out if the estate has received proper treatment. 
Fomes is the chief foe of young rubber, because it develops on 
jungle stumps soon after they begin to decay, whence it spreads to 
the roots of young rubber plants. 
Petch (4) states that Ustulina zonata is the commonest root 
disease of tea in Ceylon, and says it is specially prevalent in 
plantations in which Grevillea or Albizzia moluccana has been cut 
down and the stumps left. Ustulina zonata grows on these dead 
stumps and, spreading along the lateral roots, comes in contact 
with the roots of tea bushes which are thus infected. The fructifi¬ 
cations of this fungus are frequently found in Ceylon on dead 
stumps of Grevillea as well as around the collar of tea bushes. 
Although fructifications of Ustulina zonata have not yet been 
found on old stumps in Malaya, it is likely that the fungus often 
begins to grow on decayed stumps from which it passes to the roots 
of rubber trees. On some of the older rubber estates on which the 
disease has been found, however, very few stumps remain and it is 
possible that there are other modes of infection. The fact that 
the collar and tap root are sometimes the first parts of the tree to 
be affected, points to the same conclusion. Several of the old trees 
seen to be affected by Ustulina zonata were previously attacked by 
white ants, and it is by no means impossible that the two attacks 
are connected in some way, possibly by the ants bringing the fungus 
into the tree. With Fomes semitostus (Fomes lignosus) there are 
good grounds for thinking that white ants frequently follow an 
attack by the fungus and it is possible that the reverse process 
