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- deformed by great bark swellings which can be found on almost 
any old Hevea estate. As the swelling increases in size the bark 
bursts and displays hollows in which sometimes considerable 
quantities of latex are coagulated; whole sheets of rubber are 
occasionally found under such deformed bark. The yield of latex 
is exceptional at this stage, but tapping is almost impossible. 
utgers’s inoculation experiments showed that Phytophthora 
Faber: attacks the renewing bark, forming small vertical black 
lines above the tapping cut. This is the Line-canker (Form A), 
to be described below. 
Petch’s Observations in Ceylon. 
: Dastur’s Investigation in Burma. 
In 1916 Dastur (3) published two articles recording his 
observations on a decay of renewing bark of Hevea brasiliensis. 
The symptoms are locally known as Black Thread and are 
numerous on one cut, soon become longer and broader and appear 
in the’ new bark as black, sunken, rotten spots, sometimes with 
grey fungus on the surface. If tapping is continued they spread 
and coalesce and the whole of the new-formed bark rots away. 
It may spread inwards into the untapved bark below the cut. If 
there is continued dry weather it ceases to spread. o begin 
with, the yield of latex in this form of canker is normal]; later 
the affected cuts cease to yie ; 
na severe drought different symptoms may anvear which may 
lead to confusion. Wounds appear’ in the newly formed bark 
even with good tappers, who do not usually cut too deep. These 
are tapping wounds, as may be recognised from the fact that they 
follow the direction of the tapping. In dry weather it is not 
Possible to tap as deep as in wet weather without wounding. 
