A. Sharples 175 



the present plantations with 50-60 trees per acre, begin to decrease after 

 the trees are twenty years old. It must be remembered, however, that 

 these old areas passed through the "boom" period when the only ques- 

 tion considered was that of a maximum yield without any regard for the 

 health of the tree, and it is not possible to hazard what effect such treat- 

 ment would have. Further, root diseases on this area are giving a great 

 amount of trouble, causing continual losses. The question of the per- 

 manence of the old trees is closely linked with the possibility of root 

 diseases causing the death of large numbers. These diseases in rubber 

 plantations can be reduced to a negligible quantity if the land is cleared 

 before planting up is commenced, and though the result of clearing plan- 

 tations now in bearing is more problematical, the estates undertaking 

 this will be fully recompensed by freedom from fungus disease. 



If the fungi causing root-rots on old trees become active so as to 

 endanger the plantations at thirty years, a fresh planting scheme must 

 be considered. There are two alternatives: 



(a) Re-supplying old areas. 



To re-supply successfully the stumps, lateral roots and logs of all the 

 old trees would have to be burnt off and the ground allowed to lie fallow 

 for at least twelve months, or a subsidiary crop might be grown on the 

 land during this period. If clearing was not thoroughly undertaken, the 

 root-rot fungi would find conditions more favourable for perpetuation 

 and spread than in the previous years, and an exaggerated recurrence of 

 thinning-out conditions would result. Instead of the root-rots becoming 

 serious at ten years old, they might be expected to prove serious much 

 earlier, and numerous young trees would be killed by these fungi. 



(b) Planting new areas. 



New contiguous areas opened up near old areas containing diseased 

 trees are doomed to failure unless the latter are cleared. Presumably, the 

 old areas would be gradually abandoned, and in the interests of economy, 

 the rotting trees would be allowed to remain. Such areas would prove to 

 be centres of infection, and it is extremely probable that the new areas 

 would be quickly infected. The parasitism of these fungi may increase in 

 vigour with time, and as observations show, young plants are easily 

 attacked under suitable conditions. 



FUTURE RESEARCH. 



The evidence favours an endeavour to keep the present plantations 

 active until age prevents the old trees from yielding profitably. Many 

 magnificent looking trees are poor yield ers; this fact together with 



