560 
THE TROPICAL AGRICULTURIST. [Nov. ]. \m. 
above these spore pustules change from a 
dirty white to a pink colonr. In the white stage — 
which is the first — the spores formed are extremely small 
oval or eggshaped, and formed in chains. In order 
to afford some notion of the size of these spores — 
at a rough calculation about five million one layer 
thick would bo required to cover the surface of a 
ten cent piece. Later on from behind second and 
differently shaped spores are formed which are 
much larger— about six times the size of the primary 
Bpores — and are in the form of a cresent or bent 
cylinder and septate i.e. having a number of trans- 
verse partitions usually eight. 
If one of the small spores be placed in a suitable 
medium and kept moist iu the course of from, 12 to 
15 hours they begin to germinate, pushing out a tube 
which as it grows branches frequently often coalescing 
with neighbouring branches, and in about 00 hours 
producing spores like those from which they originated. 
Unfortunately though this method of cultivating and 
observing the growth of spores is of the greatest 
interest yet it is of less value than observing the 
growth of the fungus iu the living cacao stem (and 
this is unfortunately impassible) because the rapidity 
and vigour of growth varies according to the media 
employed. Thus in a water or gelatine culture, the 
Bpore in germinating does not behav* as it does in 
the tissue of the cacao bark, where of course the resis- 
tance to growth is greater and the nutritive material 
different. 
The method of growth of the secondary spores is very 
similar except that a number of tubes are sent out from 
the spore even sometimes one from each of the eighth 
c'lambers into which the spores are divided. As a ruU 
the crowth is not nearly so rapid. 
Both these forms of spores are technically called 
" gonidia." The fungus, however, in adnition to 
producing the simple gonidia .spores has a thinl and 
more complex fruit which will be described later called 
" sporangia." 
PllOOREBS OF TUB DISEASE. 
In order to trace the further progress of the 
disease if we leave the diseased spots still longer and 
allow tliem to spread until they either completely cover 
the bark or else go completely round the tree and thus 
" ring " it and prevent any nutrition passing up 
to the branches above, then the tree dies— the time 
taken to kill the tree depends on a number of very 
varying circumstances and conditions, viz;— the quantity 
of mycelium in the affected tissues — the vigour of 
the remain healthy portions of the tree ; the amount 
of moisture in the soil capable of being used by 
the roots; and the damage being done to the tree 
by other enemies, borers Ac. Clearly, therefore, it is 
not possible to give any exact data as to the time 
taken by the fungus to kill the tree and in my inocula- 
tion experiments (described in my interim report) 
there was the greatest diversity in the rate of 
growth even in trees apparently equally vigorous and 
under exactly similar conditions. In one case after 
the tree was inoculated and a diseased spot produced 
the area of the diseased portion increased only 
iust a noticeable distance (about i inch) every 
iday ; in the next tree experimented on the spot 
increased its area very rapidly, and in about ten days 
covered a space more than two feet long, and almost 
round the tree. In these cases, however, the difference 
in time is explicable in other ways also. In the one 
case a great many of the spores used in inoculating the 
part may have germinated, and in the other few, and 
also the condition of the cells, more or less damaged 
by the cut made for the inoculation and the quantity of 
sap they possessed, would naturally influence the 
growth of the mycelium. 
When the tree is being killed by the canker fungus, 
it exhibits all the symptoms of death from want 
of nutrition, i. e., the browning of the leaves and 
fru-t, and the gradual drying-up of the bark of 
branch and stem. Before the bark has quite dried 
the third, and more perfect reproductive bodies are 
produced. They are easily recognized with the naked 
eye as small crimson spherical bodies generally in 
clusters (Fig. 3). They are individually not so large as 
a pin's head, but a number together are easily detected 
by their size as well as their colour. 
The best place to look for these is on the cortex 
of old trees and branches cut down because dead. 
These spherical bodies are the coverings of the third 
form of spores and contain a number cf sack-like tran- 
sparent bodies which iu their turn contain each eight 
spores. These spores are larger than the primary 
gouidia spores and are uniseptate, i.e., having one divi- 
sion (Fig. 4.) 
A very large aud important group of fungi are 
characterised by the possession of these spores — asco 
spores — so called from their being enclose'l in asci or 
the sack-like bodies described above, and in many of 
the fungi in the aaci group — the formation of gonidia 
spores precedes the production of the spherical sporan- 
gia enclosing the asci. 
We have here the complete history of the canker 
fungus, which passess all its life on the cacao and pro- 
duces all its three forms of spores there. It only 
grows on the back of the stem and branches, and not 
in the root, often spreading down below the surface of 
the ground to the root, but never iavading it and never 
passing into the leaves. 
LIABILITY TO CANKLB. 
With regard to the relation of the two varieties of 
cacao grown in Ceylon, the Foreslero, with the white 
or green pod, and the CrioUo or lied with the red 
fruit, the canker — both experiments and obee^vationi 
point to the fact that the For&stero is much lesi 
attacked by the canker than the Criollo. Iu fact the 
Forastero seems more robust in resisting all the 
enemies of cacao, I have seen a fine Forastero tree 
towering many feet above its neighbours, all of which 
were Criollo, and were damaged by the wind. There 
can be no doubt that the Forastero can be brought 
to a higher state of culiivatioii here, than the red or 
Criollo, and all supplies should be of the bardiei variety. 
CLIMATIC COSniTlONS. 
With regard to climatic conditions affecting the 
canker, the matter is one on which, to a certain 
extent, a misunderstanding exists. There is a preva- 
lent idea in the case of the cacao canker as well ai 
iu other specific diseases that an unheallliy, and not 
vigorous, tree in more iinhle to the disease than one 
full of vigour, this is misleading. Ihere is no proof 
whatever that such is the case, and it might almost 
be said that the evidence points mora to the infec- 
tion of healthy trees than unhealthy ones, but it 
must always be borne in mind that the healthy trees 
when attacked fight belter against the disease and 
have more chance to overcome it whereas in the case 
of weaker plants they succumb sooner. A'o spe/rial 
predisposition of the tree is nectusarp for the altueh of the 
funyus, the only conditions needful are moisture and 
heat. The latter v^e have always in sufficiouce in this 
counti-y, aud therefore, it is the dampness as the coi.- 
diiion which varies, and which is prejudicial to the 
tree when considering attacks of canker. The easiest 
way to understand these conditions is to remember 
that for al' practical purposes the conditions necessary 
for the germination of a seed are the con- 
ditions necessary for the gtrminaiion of 
the spores of fungi. In the case of the 
canker the spores may be blown upon a tree 
during a dry period and will after being exposed to 
dry air, for some time (and of course much more 
quickly if iu direct sunlit;ht). lose their power of 
germination. If however these spores alight on the 
cortex of a tree, when the air is charged with 
moisture, and when the stem itself is damp it ii 
almost certain to penetrate and infect the tree. With 
regard to the entrance of the geiminaiing tube of 
the spore into the bark tissue?, there is hcire a rather 
difficult point to decide whether the young mycelium 
can force its way through, hitherto unbroken cortex or 
whether it must find ;in opening caused by a natural 
crack an insect puncture or a casual injury. My ex- 
perience on this subject leads me to thir.k that in 
the case of young trees or the young parts of old trees; 
the mycelium can penetrate but iu the case of thicker 
cortex on old trees there must be some opening by 
which an enti-ance can be effected. 
