A. Sharples 169 



The rapidity of the healing of the wounds in the control plants is 

 noteworthy. In Experiment 1, observations were continued for some 

 time comparing Nos. 4 and 8, in which cases the fungus penetrated slowly 

 about the wounded part, and the control plants where sterilised slips of 

 wood were placed in the cuts. Healthy callus healed the wounds in the 

 controls in two months, while the wounds in Nos. 4 and 8 showed no 

 signs of healing after three and four months. Compared with No. 6, 

 which recovered completely, the cuts in the controls healed much more 

 rapidly. The control plants in both experiments continued to flourish. 



These inoculation experiments confirm the conclusions arrived at by 

 field observations and cultural experiments. The capacity of Ustulina 

 zonata to attack either the roots or aerial parts of rubber trees through 

 wounds can no longer be doubted. The fungus makes very appreciable 

 progress in the tissues in six months' time as is indicated by the photo- 

 graphs shown, PI. VII, fig. 19 and PI. VIII, fig. 21. The common occur- 

 rence of this fungus on the plantations renders it a matter of extreme 

 import that vigorous measures should be undertaken to prevent its 

 spread. The measures to be adopted will now be considered. 



SOURCES AND MANNER OF INFECTION. 



Petch(4) states that Ustulina zonata is the cause of the commonest 

 root disease of Tea in Ceylon, and that its prevalence is due to the 

 practice of growing Grevillea among tea and cutting it out later for fire- 

 woody or when it has grown too big. The same applies when Albizzia 

 moluccana is planted through tea, and afterwards felled. The Grevillea 

 and Albizzia stumps left in the ground are rotted away owing to the 

 action of fungi, and U. zonata is the commonest one growing in them. In 

 the same way, this fungus appears to be one of the chief agents causing 

 the rotting of rubber stumps and logs left in the plantations after thin- 

 ning-out. 



On the tea plantations, the fungus enters the Grevillea and Albizzia 

 stumps and grows down them into the lateral roots. The roots of the 

 tea bushes in contact with these infected laterals are quickly attacked. 

 The same method of spread operates in the rubber plantations after the 

 thinning-out period if the stumps of the cut trees are left in the ground. 

 Lateral roots of infected trees have been traced to old rubber stumps 

 left after thinning, on which the fructifications of the fungus were 

 developing. Further, on the badly affected plantations noted up to date, 

 the stumps of the rubber trees were not removed after thinning-out. 



There is, in Malaya, a wide-spread dispersal of the fungus through the 



Ann. Biol, iv • 12 



