JajJ. 1, 1902.] 
THE TROPICAL AGRICULTURIST. 
443 
the mycelium, and in a good nntiitive solution the 
conditions of resiatance to growth and the 
amount of food available are much more favour- 
able than in the bark tissues of cacao. Oa care- 
fully searchiug diseased and dead cacao trees, and 
especially those which have been attacked for a 
louf? period, we shall find a third form of spore 
enclosed by a fruit wall, which ia very characteristic 
in colour and size. These fruits are of a bright 
crimson colour, and occur in clusters about the 
size of a pin s head ; if looked at with a lens, they 
will be seen to be in shape and colour like 
a strawberry, minute in size, about twelve or fifteen 
making a mass equal to a pin's head. 
These are the fruits or perithecia of the canker 
fungus, the name of which, botanically, is Nectria, 
and they are hollow spheres containing a series 
of sacs or "asci," which in their turn contain each 
eight spores. They are to be found only on dead 
wood or dead patches of dying branches and 
siems; 
The name "canker" is not strictly correct, though 
it may be used, as the other Nectrias parasitic on 
trees are " cankers. " Properly a canker is a 
diseas causing malformation of the tree at the point 
where the fungus is. In the case of the cacao 
Nectria, however, no such excerscence or other 
irregularity occurs, the contour of the stems of 
cankered trees being the same as those unaffected 
by disease. 
This completes the life-story of the canker fungus : 
the small oval spore producing mycelium, which in 
its turn produces spores of three kinds : first the 
oval and crescent-shaped spores in whitish masses, 
and then the ascospores enclosed in crimson spherical 
fcuits. 
INOCULATION EXPEUIMENTS. 
We have a fungus which will account for the 
diseased condition of the cacao tree, but in order 
o pro;e absolutely that this organism is the chief 
and only cause of the canker, it was necessary to 
ariiflcially produce the symptoms of the disease by 
inoculating a previously healthy tree. 
The table on page 322 gives a record of thirty- 
two inoculations made on previously healthy trees 
ID full vigour, showing the variety of the tree ex- 
perimented on, the material used to infect it, and 
the time occupied before the characteristic symptoms 
of the disease were produced. As will be seen, 
twenty five out of thirty, or more than 80 per cent., 
of the trees inoculated acquired the disease, the 
majority showing unmistakeable symptoms afcer eight 
weeks. 
As would be expected the inoculation of diseased 
tissue produces a cankered spot sooner than the 
sowing of spores in the bark, just as in the case 
of the production of new plants from cuttings instead 
of seeds. 
The time taken to affect a certain area of the 
bark is very variable; in the case of quickest growth 
(No. 13) a space of nearly 10 inches long by 4^ 
inches wide was permeated and discoloured by the 
fungus in five weeks, while in the one of slowest 
growth a piece not larger than a rupee was diseased 
after ten weeks. The spread of the canker fungus 
in the bark depends upon the amount of sap in 
the tree at the time, and in a vigorous tree where 
the roots are taking up plenty of nutrition the 
diseased spots increases more rapidly, because the 
mycelium of the fungus obtains more food. From 
the table it will be seen that in the cases of in- 
oculation of suckers only one out of three cases 
succeeded. This fact and observations as to the 
comparative rarity of canker on suckers led me to 
make further observations and experiments in this 
direction. I examined 200 suckers on 13.5 trees, 
most of which (113) had disease on stem and bran- 
ches, and in only five cases were the suckers can- 
kered. I also inoculated thirty suckers, and in only 
twelve {ifi pee cent.) waa canker produced, 
The smoothness of the outer bark on suckers an^ 
the fewness of wounds and abrasions give less 
chance for the lodgment and subsequent growth of 
Ihe cankar spores. This, together with the fact 
that even when it has a footing the spore does 
not invariably grow on them, make the " suckers " 
of more value than other brances. In cankered 
estates, therefore, whatever method has been pre- 
viously practised, it will be well to spare the sucker. 
In the limits of the Circular, though it may be 
treated in a subsequent one, it is not possible to 
discuss the pros and cons of pruning for fruit 
in cacao. Dealing with the matter from the point 
of view of combating the canker, the use of the 
knife, or, still worse, the nipping or tearing off 
suckers, leaves a vulnerable spot for the cacao 
spores, and since the suckers are more protected 
from canker than other parts, it is well to 
allow the tree to produce these branches, which 
like the lateral branches, bear their fair proportion 
of fruit. We have seen that the roots and leaves 
of the cacao tree could in no case be found affected 
by the canker fungus, and in order to still further 
prove this point I made some inoculations of ex- 
posed roots and of underground roots ; seventeen 
cases were inoculated, nine exposed roots and eight 
in which the earth was temporarily removed, but 
in none of them was any canker produced. I also 
attempted to get the spores of the fungus to grow on 
the leaves by sowing them on both the upper 
and under surfaces and by scraping the epidermis 
away and then introducing spores. Fifty of such 
experiments produced no growth of the canker, so 
that we may definitely state that the canker does not 
affect roots or leaves. 
DISEASE OF THE PODS. 
The fruit, which has so far not been mentioned 
cannot however be so classed, for upon it the fungus 
grows vigorously. For many years the great loss 
of pods in various stages of maturity has been a 
serious question. To understand the pod disease it 
must be stated that there are a number of causes 
why large numbers of pods which are set do not 
reach maturity. There are in many trees hundreds 
of pods which blacken, dry, and shrivel up when 
they are from 2-5 inches long ; in these there is 
no specific organism causing disease to be seen, and 
this is a physiological effect, it is an evil which I 
am continually observing and investigating, and all 
exact knowledge as to its nature is of importance 
as leading us nearer to some way of preventing 
this immense loss of energy in the fruit-producing 
power of the cacao tree. The planter is satisfied 
as a rule, with the comforting explanation that the 
tree has set more fruit than it can bear, and as 
he has frequently in his mind a dread of what ig 
called " over-bearing, " he is not much distressed 
at this waste. This Circular, however, treats of 
the canker, and further discussion of drying of young 
fruits must be deferred. 
The attacks of insects and other animals cause 
the death of many pods. From the squirrel to the 
Jlelopelti.f many animals feed on cacao pods or 
lay their eggs in them ; but of these I have no 
authority to speak, they are dealt with by my 
colleague, the Government Entomologist, 
The canker fungus is, however, responsible in 
many estates for a very large loss of crop. The 
disease can be readily recognized on the pod. A 
characteristic discolouration accompanied by an ex- 
cess of moisture which gives a slimy feelin" to the 
touch when cut, and as in the bark the colour is 
darkish brown, and a clear line can be drawn 
between the healthy and the diseased parts. The 
disease attacks the pod most frequently either at 
the point or at the stalk ; this is due to the fact 
that a drop of moisture in which the spore can 
germinate often hangs ou the point, and the cup 
formed round the stalk holds moisture which aida 
the growth of the spore at that end of the pod. 
Ihe life-history of the canker fungua oa th^ po(j 
