DISEASES AND PESTS 45 



cut away a narrow black streak will be found extending 

 into the wood. The black line indicates a region of 

 decay. 



" What ultimately happens depends to a great extent 

 upon the weather. If it continues wet, the black lines 

 extend upwards and downwards, and at the same 

 time increase in width. If a number of these lines 

 have arisen close together, they may coalesce, and thus 

 a wide horizontal strip of renewing cortex may be 

 destroyed. But more usually a number of parallel 

 vertical wounds are formed. When the dry weather 

 sets in, this decay stops and the wounds begin to heal 

 up. But the renewal is, in any case, rough, and where 

 several wounds have coalesced so much cortex is 

 destroyed that renewal cannot be completed for many 

 years. 



" This decay of the tapped surface is often attributed 

 to bad tapping. However, it is as a rule quite easy 

 to distinguish. Wounds due to tapping are seldom 

 vertical ; they are more usually horizontal. But there 

 is a better guide than that. When the tapper cuts 

 into the wood, he removes all the cortex overlying the 

 wound, and exposes the wood, which can easily be 

 recognized by its vertical fibres. But when this decay 

 occurs, the thin layer of cortex left after tapping is con- 

 tinuous over the wound. It is usually sunk below the 

 level of the surrounding healthy cortex, but it is unmis- 

 takably there. Even when the wounds are six months 

 old and have acquired a swollen margin, the dead layer 

 of cortex may generally be found overlying the wood 

 in the wound. 



" This decay occurs both in Ceylon and the F.M.S., 



