THE TROPICAL AGRICULTURIST. 
[Jan. 1, 1902. 
Since I have taken Dp my duties as Government 
Mycologist 1 have more than once had inquiries 
as to a' " new disease " noticed, which on speci- 
mens heing seno proved to be typical canker, and 
from its hold ou the trees and the number 
attacked must have been present iu the state for 
many mouths, probably e\en years. 
That there are also many false impressions current 
as to the nature of this disease appears in letters 
of inquiries received as well as in the local news- 
papers, which show that some of the facts recorded 
in the reports issued by the Planters' Association 
have been misunderstood. The object of this Circular, 
therefore, is to recapitulate the knowledge gained 
by the investigation and to record observations 
and experiments carried on since the reports were 
published. , 
It is to be hoped that every cacao planter, especially 
those whose experience and observation has given 
them definite views on the question, will read and 
carefully consider the evidence and the facts deduced 
therefrom. 
The methods employed in gaining these facts are 
described with a view to encouraging planters to 
gain for themselves knowledge, not by general 
observations recorded only in the memory, but by 
experiments and observations— simple perhaps in 
themselves, but conducted carefully and the results 
permanently noted. 
It say here be stated that, for reasons which 
our readers will readily understand, the names of 
states where the various observations mentioned iu 
this Circular were made are not given, yet these 
cases, like the inoculation and other experiments, 
are not mere general observations, but exact ins- 
tances, of which the place and conditions were re- 
corded at the time of observation. 
EXTERNAL EFFECTS OF CANKER. 
The first question in investigating any disease is 
—What is the nature of the departure from the 
normal health of the trees? Briefly, in the 
disease in question the external signs are a lack 
of vigour in producing fruit and leaf, similar in its 
appearances to the lack of vigour caused by long 
periods of drought or by severe mechanical injuries 
to stem or root. The period during which the tree 
continues to exist depends on the amount of disease 
on the tissues and the quantity of nutrition the 
roois can take up. The fact that trees of all varieties, at 
all ages above three or four years and in some 
cases less than that, in the best soils as well as 
on poor land, in various aspects and at different 
elevations, are attacked naturally leads to the sup- 
position that this disease is not due to conditions 
under which the trees are growing, but to the effects 
of an extraneous parasitic organism. 
No injuries caused by insect or other animal can 
be found exclusively on diseased trees, so that the 
disease cannot be due to the attacks of an animal. 
The next point is— What portion of the tree, if 
not the whole tree, is affected, and in what man- 
ner ? The roots of badly diseased trees show no 
sign of injury, and when the tree is cut down 
near the ground healthly suckers are formed, which 
grow without any sign of disease. These, as well 
as many other facts which will appear in the course 
of the Circular, show that the root is not affected 
by the disease, and it is indeed a happy thing for 
the cacao planter to be assured on this point, as root 
diseases are much more difficult to battle with, and 
consequently much more to be feared. 
The leaves of diseased trees, except in rare cases, 
are free from fungi, and present on microscopic 
examination all the features to be found in leaves 
dying from want of moisture, showing that there 
is no disease in the leaf, but that some malady 
in another part of the plant has cut oS their supply 
of nutrition from the root. 
The stem aud branches must now be examined, 
and here it is not hard to find the cauLe of the 
cliaeaso. Li we exammo the ei^terual bark of the 
* em and branches of diseased cacao trees, we 
^ball notice darker pate hes, where in some cases 
(where there is an injury in the bark, and inject 
puncture, or an abrasion) claret coloured drops 
exude, and where they have run down and dried 
up a rusty coloured streak is seen. On scraping 
these darkened patches the ba'k is found to be 
discoloured, sometimes of a deep claret hue, but 
in earlier stages of a brownish or " neutral tint " 
colour, quite evident if these places be compared 
with the yellow or reddish yellow colour of healthy 
cacao bark. This discoloured bark is always very 
wet, and on being cut exudes copious moisture — 
the darker the colour the more the moisture— 
and feels soapy to the touch. If such a diseased 
patch be carefully shaved, its difference from the 
healthy bark surrounding it can be clearly seen, 
as it stands out as a bright claret coloured patch 
surrounded by the light yellow healthy tissue. 
MICROSCOPIC CHARACTERS OF THE DISEASE. 
A microscopic examination of the tissue in these 
discoloured parts shows a quantity of mycelium of 
a fungus permeating the tissue. 
Mycelium is the vegetative portion of a fungus, 
that is to say, it is to a fungus what the root, 
stem, branches, and leaves are to a flowering 
plant. The quantity of mycelium is much greater 
in the darker coloured parts than in those of a 
neutral tint, and in cases where the discolouration 
is only just perceptible the mycelium is scanty. 
The mycelium also penetrates into the wood of 
the stems and branches, running generally in a 
longitudinal direction. It can be observed when 
it is present iu any quantity as a thin black strand 
as thick as a piece of cotton ; this strand may 
crop out into the bark at another place higher up 
or lower down, and produce a fresh cankered spot 
on the bark, The time the fungus takes to kill a 
tree or part of a tree depends upon many condi- 
tions. It is possible for it to produce death in a 
few months: as a rule it takes two oi three years. 
Death occurs when there is sufficient mycelium to 
prevent any sap being conveyed from the roots to 
the parts above. 
To return to the external appearance of the 
cankered tree. If we observe a number of patches of 
disease we shall find on many of them whitish 
pustules on the surface of the baik, varying in 
size from that of a pin's head to a ten-cent piece 
white gray or pinkish gray in colour, and bursting 
through small ruptures in the bark. If these be ex- 
amined microscopically they will be seen to consist 
of masses of oval-shaped bodies, and some larger 
bodies crescent-shaped and septate, i.e., having a 
number of partitions, usually eight. They are the 
spores of the fungus, and a section cut through the 
centie of one of these masses into the discoloured 
bdik will show that they are produced on the 
mycelium which permeates the tissues. Spores may 
for purposes of popular explanation be considered 
as the seeds of the fungus. These spores are ex- 
cessively minute ; some notion of their size may be 
gained by the rough calculation that about live 
million could be placed on a ten-cent piece only 
one layer thick ; those which are crescent-shaped 
are larger, being about fix times the size of the 
oval spores. 
When these spores are sown in a suitable medium 
and kept moist (a form of microscopic gardening 
which must be always used in gaining a knowledge 
of these small organisms), in the course of twelve 
or fifteen hours they begin to grow, pushing out a 
tube, which, as it grows, branches, frequently coalesc- 
ing with neighbouring branches, and in about fifty 
hours producing more spores similar to those from 
which it originated. This minute gardening is of 
great interest, but it is of less practical value than 
observing the processes of growth in the living 
cacao tissues (which is unfortunately impossible), 
because the nature of the " bed " in which the spores 
^re growing affects the rapidity and chareicter of 
