P. T. Brooks 219 



The part of the tree chiefly ;i Ifected is t lie collar which is usually attacked 

 first on one side only, the hark collapsing. Neighbouring lateral roots 

 and the tap root often become affected in the same manner and in 

 advanced cases the disease may spread up the trunk to a height of three 

 or four feet. If the diseased tissues are exposed, conspicuous black 

 lines are often seen near the limits of the affected parts although these 

 lines are not invariably present. The absence of external mycelium 

 and of rhizomorphic strands between the bark and the wood distin- 

 guishes this disease from other well-known root troubles of Hevea. 

 As the fungus progresses in the collar and root system of the tree the 

 foliage becomes thin, the branches die back, and the whole tree succumbs 

 unless successfully treated. 



The fructifications of the fungus appear as closely adpressed plates, 

 grey brown to blackish in colour, on the collar and exposed lateral roots 

 of affected trees. The fructifications are easily overlooked, especially 

 in wet weather when they become splashed with mud. The conidial 

 stage present in young specimens of the fungus in Ceylon has not yet 

 been found in Malayan specimens although adult fruit bodies are 

 undoubtedly identical. The mature plate-like fructifications which 

 may be several inches across are marked by an irregular and 

 obscurely zoned surface punctured by minute dots. If the grey brown 

 surface of a fruit body is scratched, a black layer is seen which may also 

 become exposed by the natural wearing away of the thin covering. 

 Below this black layer the perithecia are formed from which the spores 

 subsequently exude in black masses. 



Wood and bark invaded by the fungus become discoloured. The 

 black lines often found near the margin of the affected tissues are 

 caused by the aggregation and darkening of the hyphae which form 

 a kind of sclerotic plate in the cells of these regions. Pure cultures of 

 the fungus were established on blocks of Hevea wood in which similar- 

 black lines were formed. It is only when black lines in the tissues 

 are associated with an extensive affection of the collar and root system 

 of the tree that Ustulina zonata should be suspected, as two other fungi, 

 Nummularia pithodes (B. and Br.), Petch, and a species of Xylaria both 

 belonging with Ustulina zonata to the Xylariaceae and both common 

 saprophytes on dead rubber wood, produce similar black zones. Inocula- 

 tions of the roots of seedling Hevea plants and of 4 year old trees, just 

 below soil level, with material of the fungus growing in pure culture were 

 followed by the establishment of the fungus in the tissues, some of 

 the seedlings being killed in consequence. 



