166 Ustiilina Zonata {Lev.) Sacc. on Hevea Ri'asilieiisis 



Fertile fructifications have not yet been obtained in agar cultures. 

 Small rhizom'orphic-like strands which attain a height of I" above the 

 surface of the culture are often found (PI. VII, fig. 18). These strands 

 resemble the individual components of the lichenoid form of the fungus. 

 They grow about in the culture medium in a very irregular manner, and 

 are doubtless comparable with the black lines running through the rotten 

 wood of plants affected with U. zonula. 



These experiments prove that Ustulina zonaUi is the fungus largely 

 responsible for the death of trees attacked by borers. Attacks by boring 

 beetles would not prove serious if other agencies were not concerned. The 

 connection between the insects and this fungus, which is the cause of one 

 of the most serious diseases on old rubber we shall have to contend with 

 in Malaya, renders the question of the control of collar-rot a difficult 

 one. It is obvious, however^ that strict attention must be given to all 

 trees, stumps or logs in which borers are working. 



FUNGUS IN THE WOOD. 



The progress of the fungus in the tissues is well shown by Fig. 19, 

 which shows an artificial inoculation at the collar. The fungus advances 

 from the point of inoculation into the wood and spreads more quickly in 

 this than in the bark. The wood assumes a brown colour as the fungus 

 advances, this discoloration extending fairly evenly in- the vertical and 

 lateral directions. Attention may be called to the apparent zoning shown 

 by the discoloured tissues. 



The brown wood is permeated with thin hyaline hyphae largely con- 

 fined to the medullary rays and fibres of the wood. The vessels are com- 

 paratively little affected; only when the black lines cross the vertical 

 path of the vessels are hyphae noticeable in them. 



The fungus causes a drying of the affected tissues ; the wood becomes 

 crumbly and falls apart under the pressure of the fingers in advanced 

 cases. The black lines of fungus tissue appear as the affected wood dries. 

 These lines are formed by the aggregation and massing of hyaline hyphae ; 

 this aggregation always commences in the medullary rays (PI. VII, fig. 20). 

 Later, tracts of connecting cells between the rays become filled with 

 similar tissue, and a continuous line is formed. Carbonaceous material 

 is deposited in the cells after aggregation, and as time passes it is often 

 difficult to detect their origin. The elements bordering the lines are 

 crowded with hyaline hyphae. 



The. slow progress of the fimgus in the root system is connected with 

 its method of penetrating the tissues. The vessels are the routes along 



