A. Sharpies 159 



its branches come in contact with and bruise the branches and trunks of 

 neighbouring trees, wounding the outer corky layers. Through these 

 places boring beetles enter and the fungus U. zonata may be taken in by, 

 or quickly follows the insects. The fungus penetrates the wood quickly, 

 for the insects bore to every part of the tree carrying small pieces of 

 diseased tissue, so setting up innumerable centres of infection. The fructi- 

 fications form on the surface of the diseased parts, and spores from these 

 are blown about the plantation. The rubber logs and stumps lying about 

 the thinned-out areas form suitable growing places, as does any rotting 

 soft-wood timber, and thus the fungus obtains suitable conditions for 

 perpetuation and spread. 



When a tree attacked by borers is examined, the typical symptoms 

 caused by U. zonata can nearly always be demonstrated. The association 

 is probably due to the fact that a tree penetrated by borers is very liable 

 to attack from common wound-fungi. Ustulina zonata is a wound para- 

 site on Hevea hrasiliensis, and is also one of the commonest causes of 

 rotting in soft-wood timber in the plantations. Its prevalence on the 

 plantations in rotting timber and stumps increases its chances of attack- 

 ing rubber trees whenever a suitable opportunity occurs. The fungus 

 often gains an entry through wounds caused by the breaking of large 

 branches. In these cases, there is always a copious exudation of latex for 

 a lengthy period as fresh areas of healthy bark are attacked during the 

 progress of the fungus. It passes much more quickly through the wood 

 than the bark. It would appear that Ustulina zonata does not easily 

 attack rubber trees unless an exposed wood surface, or a convenient path 

 to a wood surface, as in trees penetrated by borers, is provided. 



Fructifications are found on all parts of the stem and branches where 

 the fungus is working in the tissues. "Stag's head" in rubber trees is a 

 well-known phenomenon and is usually attributed to Diplodia sp., the 

 cause of " Die-back." On two occasions the fruit-bodies of U. zonata have 

 been observed growing on these dead branches taken from the topmost 

 parts of the tree. When the fungus gains an entry through wounds 

 caused by the breaking of large branches, a large quantity of fruit is 

 usually produced about the place of entry; the later blackened stage of 

 the fructifications are often masked by a copious exudation of latex from 

 the diseased portions. 



It is possible that borers may directly transfer spores to the trees they 

 enter. Insects such as White ants, Red ants, etc. walking over the flat plate- 

 like fruit-bodies when the latter are producing spores would carry away 

 numerous conidia or ascopores attached to their appendages. Fructifi- 



