518 
THE TROPICAL 
AGRICULTURIST, 
[Feb. 1, 1902. 
diseased tissue and a wide margin should be entirely 
excised. " This has been carried out on many 
thousands of trees. I have personally visited more 
than forty estates where disease is prevalent, and 
on many of Which trees have been so treated, and 
from observations jotted down in my field note-booka 
I estimate that in practically all cases where it 
was carried out carefully the disease has been entirely 
eradicated at that spot. In a proportion of the cases 
the treatment led to the death of the tree, as the 
canker had grown for so long in the bark and 
permeated so large an area that cutting it out left 
no connection at all between the roots and the 
leaves of the tree, which is essential to life. 
The coat of this treatment has naturally varied 
on different estates according to the amount of the 
work and the skill with which it has been done 
by the coolies, also naturally accoding to the amount 
of canker existing in each estate treated. The maximum 
amount spent in this work on a peviously badly 
cankered estate has been less than Rs. 15 per acre 
in a year, and in the majority of cases a much 
smaller sum than that, Such work, the only in- 
surance possible agaianst damage in an estate at 
present free from canker, should cost under Rs. 3 
per acra in the year. 
In considering this matter of curative means two 
things must be remembered : First, that the presence 
of mycelium does not always show itself by a dis- 
colouration. The brownish and claret colours are 
only produced when there is an immense amount 
of the mycelium of the fungus in the tissue. In 
the early stages of a diseased patch the chance in 
colour of the tissue is almost imperceptible, aod the 
absence of discolouration must not be taken aa 
meaning absence of the fungus mycelium. Second, 
the mycelium may be present in such quantity aa 
to cause a patch of distinct discolouration, but the 
tissue surrounding this patch also contains my- 
celium, though in less quantity. It, however, this 
is left bahind, the patch will spread again. It is 
thus essential to cut a wide margin round the dis- 
coloured spot of at least 2 inches. I have observed 
many patches cut out partially, i.e., all the claret 
colour taken away, which a few weeks later showed 
signs of living and spreading mycelium at the 
Bides. Even when the patch has been vigorously 
and carefully treated the tree should be some weeks 
later again examined to aee that the f aagaa has been 
entirely removed. 
A second element of danger which requires care 
is the habit of the fungus — previously mentioned— 
of penetrating to the old wood of the tree growing 
up behind the bark, running longitudinally along 
the tree, and cropping out at another place above 
or below the initial patch. This has been on one 
estate most carefully searched for and eradicated 
in a way that reflects great credit on the aptness 
of the cooly to carry out skilled work when taught 
well how to do it. The mycelium can be detected 
in the wood behind a patch of canker as a blaok 
line about the thickness of a piece of thread, which 
runs sometimes for more than a foot up or down the 
stem. 
Three years' trial of cutting out cankered patches 
in cacao trees in Ceylon has, 1 think, proved to all 
observers that this method of dealing with the 
disease is at once practicable and efficient. When 
one comes to examine carefully cases of cankered 
patcliea said to be cut out and still spreading, the 
explanation, aa a rule, is that the fungus mycelium 
was not entirely removed, or that a fresh inocula- 
tion by a new spore has begun the canker at the same 
place or near it. 
Tkeatment of Cankbbed Trees : Shaving. 
The cutting out the cankered tissue entirely was,, 
however, too drastic and too expensive a cure for 
Bome planters, aa in some badly diseased estates it 
would have killed a large proportion of trees, and 
in my reports of 1898 I recommended as an alter- 
pativ* method, though not promising such gooci 
results, the shaving of the affected parts and allow- 
ing the shade to be light enough for the sun to 
dry up these shaved parts. This has proved suc- 
cessful, but aa was expected not so entirely successful 
as the more thorough cutting out. In cases of 
estates where shade was light and the sun got free 
access this light shaviug has freed the trees from 
disease in more than 50 per cent, of the cases 
treated. 
The explanation of the success of this method of 
shaving in eradicating canker is that the mycelium 
of the fungus is cut, broken, or bruised at countless 
places by the shaving knife (or what is still better 
for quickness and clean work, the spoke-shave), and 
with the drying effect of the sun on the tissues it 
cannot recover itself, and dies. Though many of 
the cells of the bark are killed, a portion of them 
are active below the surface, and ihe tree does not 
suffer very seriously from the operation. 
If this treatment is carried out under dense shade 
or in damp weather, the effects are seldom good, 
and in the majority of cases the fungus is not 
eradicated. Some interesting experiments have been 
brought to my notice of an artificial he^t being 
applied to the shaved surfaces, charcoal braziers 
being held within a few inches of the newly-shaved 
surface, and the results of this were almost as 
marked as direct aun light. 
1 tried this process on a small scale ou four 
trees, and in the parts shaved and scorched (one of 
whicli was 13 inches by 10 and nearly encircling 
the tree) the mycelium was killed, and the bark 
tissues were not entirely killed, so that in a short 
time the trees recovered entirely from the disease. 
Though this " hot potting " is almost equal in 
its results to the effect of the sun, it is not so 
good, because it is too local ; and unless very care- 
fully carried out there is too much scorching, and 
the tissues are damaged to a great extent. The ex- 
periment is, however, interesting, as showing the 
■modus operandi of the cure after shaving. The 
moisture is dried up, and the mycelium of the fun- 
gus cannot get sufficient supplies of nourishment 
to counteract the great damage done, while the 
plant tissues below, which are unhurt, drawing 
their supplies eventually from the root, gradually 
recover. 
Tebatment foe Pod Disease. 
The eradication of the canker in the bark is of 
vital importance, but of no less importance is the 
removal of diseased pods. As was stated previously 
the fungus spreads and produces its spores ten 
times more rapidly in the soft tissue of the pod 
than in the bark, so that prompt measures must 
be taken if the spreading of the canker fungus 
by means of the pods is to be prevented. All diseased 
pods, however slightly affected, should be st once 
removed and the husks burnt, or if that is 
impossible during wet weather, buried withlime, 
By this means a very great, if not the greatest, 
source of infection is destroyed, and no loss accrues 
to the estate, as the value of the pods (even though 
unripe) with a small patch of disease is greater 
than a few days later, when they are entirely 
diseased and the seeds also blackened. The unripe 
and partially diseased seeds produce "black cacao" 
ibut tbe pods which are left till the disease has 
spread entirely over them are often unfit even for 
" black cacao. " 
The simplest method of carrying out this import- 
ant work is to have all diseased pods, however 
little affected, collected when the ripe pods are being 
plucked, and to send round at periods between the 
plucking times, and have any which have since 
acquired the disease taken away. In this way no 
pod could remain on the tree diseased for more than 
four or five days. This could be done at a very little 
cost. 
All these preventive and curative means, cutting 
out, shaving, and destroying diseased pods, should 
done during tbs dry weather as far aa po^ible) 
