THE TROPICAL AGRICULTURIST. 
Dec. t, 1897.] 
Bent in the different pieces of bark suggest a funpis 
as the cause of the disease, and furthermore, that 
the fungus belongs to the group causing root dis- 
ease. If the roots of a diseased tree are removed 
and portions kept moist under a bell-jar, the charac- 
teristic snow-white nodulose mycelium would in all 
probability cover the roots in a few days. 
The sporophores* of such fungi are only produced 
on dead end thoroughly decayed host plants. 
The two conditions favouring the spread of root 
disease are : (1) accumulation of humus, f &c., on 
the ground, which retains moisture and favours the 
spread of the mycelium from tree to tree; (2) o\er- 
head shade. 
Diseased trees should be isolated by narrow 
ches, 8 to 10 inches deep. These retard the spread 
of the mycelium. The removal of the roots of dead 
trees and sterilization J of the soil (by fire, &c.) is 
most important. 
Ascertain if the disease attacks native trees, may 
be in a modified form. — G. Masses. 
It will be seen from the above that the 
home authorities regard the fungus as one of 
the class of root-disease fungi. Without the 
reproductive organs, the exact indentification of a 
fungus is all but impossible, and until quite lately no 
sign of such organs has been discovered on any of the _ 
diseased cacao. 
It is obvious that if the canker on the stem be merely 
an indication of diseased roots, the treatment recom- 
mended in the preceding Circular will have to be 
modified i mere removal of diseased parts of the stem 
will be evidently only a temporary measure. 
Most observations made in Ceylon seem to contra- 
dict the supposition of its being a root disease, and 
the publication of this Circular has therefore been 
delayed for further investigation of the subject It 
so happens that the group of fungi causing many 
of the bark cankers of trees is very closely allied 
to the group causing root diseases. 
These bark canker fungi as a rule can only 
enter the stem by way of wounded surfaces on 
the bark, but a very slight wound is often 
enfficieni. The frequent connection of the 
cacao canker with wounded places has been pointed out 
in the preceding Circular. 
Reproductive organs which appear to belong to the 
fungus causing the cacao canker have recently been 
discovered on the bark of the stem, and indicate that 
the fungus does belong to one of the two groups just 
mentioned. As no sign of these organs can be found 
on the roots, and the mycelium mentioned in Mr. 
Massee’s report has not been seen on roots treated 
in the way there described, it seems more probable 
that the canker is only a bark and not a root disease. 
Again however the final decision of this question re- 
quires experiments in the infection of healthy trees, 
(fee., which are now being carried on at Peradeniya, and 
also further reference to the authorities at home, 
it has been decided to publish this Circular without 
further delay. , 3 . 
The presence of the disease, as stated rn the pre- 
ceding Circular, is largely connected with insufficient 
drainage, and Dr. Morris’s recommendations on 
this subject deserve careful attention. In 
many cacao plantations in Ceylon the soil has 
become sour through insufficient drainage, and the 
application of lime in some of these cases has been 
most beneficial. 
Besides its action in removing the sourness of the 
soil, the application of lime helps to kill the fungi 
that may be present, and is therefore much to be 
recommended. 
* The spore-bearing organs of the fungus : the 
spores are the detached portions which reproduce the 
fungus ; placed under suitable conditions a spore 
germinates and gives rise to a new mycelium. 
f Decaying organic matter, whether of animal or 
vegetable origin. 
I The killing of all living matter : spores, myce- 
lium, &o. 
4$t 
Dr. Morris’s remarks on shading should also be 
noted. Mature cacao can do with very little shade 
from the sun, but requires protection from wind. In 
the Botanic Garden at Anuradhapura the Forastero 
cacao does excellently with practically no overhead 
shade at all, hot and dry though the climate is. The 
shade in most Ceylon plantations was provided to 
avoid the attacks of Helopeltis, and now that the 
trees have grown very large it is probably 
denser than is necessary for that purpose. 
The reduction, if made, should be very gra- 
dual, otherwise the sudden increase of the crop 
will tend to weaken the trees. This reduction would 
act upon the fungus causing the canker in two ways ; 
by drying the soil and thus helping to prevent its 
getting sour and so weakening the trees, and by the 
direct action of the sunlight, which checks the growth 
of fungi and is often fatal to fungus spores upon 
which it acts. Care should be taken to see that 
cacao is well sheltered from wind : not merely is 
wind harmful to the plant itself, but it also carries 
the spores of disease from one plant to another. 
The period at which further spread of the disease 
usually takes place is now approaching, viz., the wet 
weather of the north-east monsoon, and especial 
care should be taken to destroy as far as possible 
all diseased trees, and parts of trees, to prevent 
the disease extending. The reproductive organs both 
of root and bark diseases are produced only on dead 
and decaying parts of diseased trees, and if there 
reproductive organs can be destroyed, or prevented 
from forming, as the case may be, the disease will 
thus be prevented from spreading to fresh trees. 
To this end it is essential that the destruction be 
hy fire, which alone is certain to kill the fungi. Also, 
the destruction should be on the spot where the 
diseased tree grew. If infected trees or parts of trees 
are carried about the estate, they will spread the 
disease as they go by scattering the fungus spores. 
For the same reason coolies should be prevented from 
going amongst healthy trees immediately after work- 
ing amongst diseased ones. They should wash 
themselves before doing so. It would be advisable to 
employ a separate gang of coolies in working with 
diseased trees. 
All diseased trees should be cut down to the ground, 
or better rooted up, and burnt upon the spot, and at 
the same time all the dead leaves and other rubbish 
lying round about them should be burnt. The surface 
soil should be turned over and treated with lime 
and the ground left fallow for some time. If planted 
again in cacao, Forastero varieties should be employed 
(see remarks on pages 10 and 11 of the preceding 
Circular). 
On estates where the disease is widespread it would 
be well to burn all the dead leaves and lime the 
soil, as there will probably be fungus spores lying 
on the ground ready for germination in all parts of 
the estate. 
In dealing with diseases caused by parasitic fungi, 
the aim is prevention rather than cure. Once a 
tree is fairly attacked cure is usually impossible, and 
it is best to kill and destroy it. 
In the neighbourhood of diseased trees not merely 
the soil, but also the surrounditg healthy trees (in- 
cluding of course the shade trees) will be more or 
less covered with spores of the disease. Those on 
the soil may be killed by the lime treatment above 
described, but considerable danger remains from those 
on the trees, which under favourable conditions 
will germinate there and produce furthsr attacks 
of the disease. These spores may be killed by 
the application of various fungicides. The best 
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