Disease of Rubber caused by Ustulina Zonata. 153 
diseased tissues are exposed, conspicuous black lines (cf. Fig. 1) 
about inch in diameter are often seen near the limits of the 
affected parts, though these lines are not invariably present. These 
narrow black zones occur more frequently in the wood than in the 
bark and their course is rather irregular. No external mycelium 
has been found associated with roots suffering from this disease, 
hence it is readily distinguished from the root troubles caused by 
Fig. 1. Ustulina zonata. Piece of rubber wood taken from the collar of 
an affected tree shewing black zones (natural size). A, long black zone near 
limit of diseased wood. B, small black zones forming islands some distance 
from the chief black line. C, diseased wood with brownish discolouration. 
Fomes semitostus (Foines lignosus) and by Hymenoclicete noxia. The 
absence of rhizomorphic strands between the bark and the wood 
distinguishes the affection from that caused by Sphcerostilbe repens, 
the black lines in the tissues often associated with Ustulina zonata 
being chiefly found in the wood and differing in nature from rhizo¬ 
morphic strands, as will be shewn below. 
This disease, which is by no means uncommon in Malaya, 
principally affects old trees, and some of the finest specimens of 
plantation rubber 14 to 16 years of age have succumbed to it. A 
few trees 5 to 6 years old have also been attacked by it. The 
disease has been found both on flat and on undulating land in 
