517 



F : "I send some of the dead trees. They 



were sixteen months old and grew on flat well drained land 



the trees were together, but neighbouring plants look quite 



healthy." 



When a tree, which has been killed by this root disease, is pulled 

 up, the cause of death is at once apparent. In many places there is a 

 cobweb-like felt of whitish fungus, but in parts the fungus threads 

 (mycelia) are closely aggregated in straw-coloured strands, like stout 

 cord, stretching somewhat irregularly over the surface of the root. 



If incisions are made in the tap root and stem, a discoloration of 

 the wood will be observed in the former, but not in the latter except 

 occasionally for a little way above the collar. 



Method of Attack. 



Some planters maintain that the tap root is first attacked. Con- 

 sidering the method of planting and for various reasons this seems 

 unlikely; as far as I have seen the lateral roots, and only those near 

 the surface, are the first to suffer. The deeper lateral roots, or at least 

 their extreme ends, are mostly free from fungal threads even when the 

 tap root is already covered with them. Often the tap and lateral roots 

 over one side only have been choked by the mycelia, the lateral roots 

 on the other side being free. In such cases the side on which the 

 diseased roots lie is always next a jungle stump. On different occa- 

 sions I have traced the mycelia along lateral roots to decaying jungle 

 stumps. It may be taken as pretty certain that these stumps and logs 

 are the original source of trouble. It is mostly impossible to identify 

 them, but on more than one occasion I have found Meranti {Shorea 

 sp.) and Merbau {Afzelia palembanica) offenders. The lateral roots of 

 the para tree spread so fast that in a year or little more all jungle 

 stumps are in contact with them. But a root may be attacked before 

 reaching an infected stump as the fungal threads can travel for some 

 distance through the soil. 



The only occasions on which I found nursery plants attacked was 

 when the nursery had been badly cleared and old stumps had been 

 left in it. I may mention that in many of these nurseries the respec- 

 tive managers had not suspected the presence on their young plants of 

 anything inimical. They were all quite healthy in appearance, but 

 would have succumbed when planted out, and each diseased plant 

 would have served as a centre -of contamination from which healthy 

 plants would have been infected. 



Identification of Fungus. 



Fructifications (fruits), such as the usual "bracket mushrooms" 

 found in abundance on the dead logs and stumps of a clearing, have not 

 been noticed in association with this disease, nor has it produced 

 spores (seeds) notwithstanding numerous infection experiments and 

 long continued cultures in various nutrient media in the laboratory, 

 consequently it is impossible to give it a scientific name, an omission 

 which from the planter's point of view is not of much moment. It is 



