262 PflYTOPHTHORA MEADH 11. Sp. ON HEVEA BRASILIENStS 



have partially died back, (2) that oospores, which are resting-spores, are found 

 in the fruit, and (3) that the fruits are the main propagating centres for multi- 

 plying the fungus. This suggests that the branches that have died back, and 

 the fruits, should be dealt with. In the one case the aim is to stop the fungus 

 from beginning its activity in the new season, and in the other to stop its rapid 

 propagation after it has once begun. If all branches that this fungus has 

 caused to die back were removed, say, a foot beyond the junction of living and 

 dead tissues, many of the centres of infection that begin the new attack of the 

 fungus each year, would be destroyed. Now all branches that die back on 

 Hevea do not do so because of this fungus. There are other factors that produce 

 die-back, e.g., shade causes the lower branches to die, and other fungi, e.g., 

 BotryoMplodia theobromce Pat. and Glceosporium alborubrum Fetch, also do so. 

 There is no simple field method of distinguishing between these various causes, 

 so that, if die-back branches are to be removed, then all will have to be removed 

 irrespective of the causative agent. Many of the branches that have died 

 back are mere twigs, while others are larger. There are many such on each 

 tree— far more than is realized till the necessity comes to remove them — and 

 they are scattered over the tree indiscriminately. To remove them to a very 

 large extent is possible, but to do it thoroughly will certainly be costly. The 

 cost, however, would be greatest in the first year, and would rapidly decrease in 

 succeeding years, presuming that this method is found efficacious and is 

 continued. 



It has also been shown that the fungus may invade a branch along the 

 fruit-stalk, and that the fruit-stalks of rotted fruits may remain on the tree 

 through the dry weather till the beginning of the monsoon. This is a real 

 difficulty in the way of preventive measures, for it is impossible to remove 

 every possible centre of infection of this kind. Even if all these old fruit-stalks 

 were removed when the trees are bare in December-January, there is the fact 

 that the mycelium of the fungus invades the branches from which the fruit- 

 stalks spring at their point of insertion. Kemoving die-back branches 

 would not destroy this source of re-infection entirely. 



Removal of the fruits before the break of the monsoon, or at the latest 

 during the first fortnight of the monsoon, though this is cutting it rather fine 

 for safety, would stop the rapid propagation of the fungus that begins about 

 15 days after the monsoon has set in. This would also for future infection 

 get over the difficulty mentioned in the last paragraph with regard to infection 

 by fruit-stalks. If the fruits are not there to become infected, the fruit-stalks 

 would not carry the mycelium of the fungus into the branches. To remove 



