in 
THE TROPICAL AGRICULTURIST. 
[Jan. 1, 1902. 
is similar to its progress in the bark, except that 
it is niucli shorter. We liave seen that under 
favourable conditions the time taken from the ger- 
mination of the spore to the production of new 
spores in the baik is a question of some weeks 
and often months, but the whole of this is pissed 
in the pods in a few days, and vast niinihjrs of 
spores aie produced in every pod that is allowed to 
hang on the tree for a week or more. 
The diseased tissue of the pod if examined micros- 
copically will be found to be permeated in the 
same way by the mycelium of the fungus, but this 
mycelium is of a more luxuriant chaiacter, because 
there is more moisture in the pod for it to grow 
on and less resistance to its growth. 
If a planter wishes to observe for himself the 
life-history of the canker fungu?, he can by placing 
a cankertd pod under a glass and keeping it from 
drying up see the production of the two early forma 
of spore (gonidia), and later the red spherical bodies 
of perithecia containing the ascospores. 
That the canker fungus grows on the pods has 
been proved by numerous observations, and in order 
to test by inoculation I experimented with twenty 
pods of fairly typical Red Cacao trees and twenty 
of Forastero trees. These I inoculated with both 
gonidia and ascospores, seventeen of each variety 
being painted with gonidia spores and three of 
each kind with ascospores. In the case of the Red 
Cacao all the seventeen grew at once, twelve in 
the first three days and the rest within eight 
days ; in the Forastero twelve grow within nine 
days, the remaining five did not acquire the disease, 
the fact that the typical Forastero fruit has a thicker 
epidermis or outer skin no doubt gives it a greater 
power of resistance to the growing spore of the canker 
fungus. 
On all these inoculated pods the spores- both 
gonidia and ascospores —of the fungm were produced 
in from four to nine days, and these spores were 
exactly similar in character to those on the bark. 
BELATION BETWEEN POD AND STEM DISEASE, 
In order to prove the relation between the canker 
on the bark and on the pods, and how far the one 
spreads to the other, the following experiments were 
made : — 
(1) Small piecas of cankered bark were placed 
in selected healthy pods on sound trees. Five pods 
were so treated. In all cises the pods became 
diseased after eight days, and in less than four- 
teen days spores of the fungi were produced in 
abundance. 
(2) Small pieces of diseased pods were placed in 
the bark of sound trees. Bight of these inoculations 
were made. In all cases canker was produced In 
the bark after ten days, and the spores of canker 
Were found after eighteen days. 
(3) Small pieces of cankered bark were placed 
in the bark of sound trees just above the stalks 
of healthy pods. Seven inoculations were made. In 
all cases the bark became diseased, and it spread 
to the pods, which were plainly diseased, in nine 
days, and spores produced both on the pods and 
on their stalks. 
(4) Pieces of diseased pods were placed in healthy 
pods on sound trees. Six of these inoculations were 
made. All the pods became diseased, and in 
three cases the canfier spread through the stalk to 
the adjoining bark ; in the other three cases the 
stalks of the pods were cankered, but not the 
adjacent bark. In one case the mycelium of the 
canker went through in to the wood of the tree 
through the stalk without affecting the adjacent 
bark. 
Wo learn from these experiments that the canker 
fungus cati Bprcad fiom the bark of stems or branches 
to the pods ; that the fungus can spread from the 
pod to the bark of stem or branch. 
Another matter of interest in connection with 
the disease on the pods is that they are invaded 
auothe'^ lungus I'liytoijUthora, fp; one which is 
common in many climates and grows on the soft 
tissues of numerous plants Oa examination of 
some hundreds of diseased cacao poas I aiways 
found tbis fungus associated with the canker fanens 
I was unable to get a pure culture of the spores of 
he second fungus, so that I could not observe 
the action of the Ph,,tophthora alone on the pod 
i:he canker fungus I have found by itself on the 
pod, but in the great majority of cases it is soon 
joined by the Phutophthora, and this latter I have sever 
louud by Itself lu the pods in nature 
A very large series of observations of the rela- 
tion between the canker in the biik and on the 
pDd3 shows that in a certain proportion of cases 
the canker originates in the bark from a cankered 
pod which has been left on the tree sutficiently lone 
-three or four days— to enable the mycelium to 
penetrate through the stalk; aho in aXllerprS 
portioa the c.i.ker in the pod has been caused 
by the mycelium growing from the bark through 
the stalk and infecting the pod 
To sum up the knowledge gimed by this investiga- 
tion of the cac.o canker. The disease is due to a 
fungus ^^,ectrla) frowing iu the bark '•wood" and 
pods of the cacao tree. It spreads by means of an 
abundant production of spores of thiee kinds It 
grows more rapidly on the pods than in the bark 
and Its rate of growth in both cases is regulated by the 
SZ. '''''' ^-'dlX 
( To he concluded. J 
SOME RECENT INVESTIGATIONS IN 
THE CHEMISTRY OP AGRICULTURE. 
(Continued Jrom page 381.) 
Soil BIoistuke. 
I must now refer, though with great brevity, to 
another department in the investigation of soils 
namely, the Jloistwe conditions. ' 
This subject has a particular interest in India 
where the rainfall is unequally distributed 
Some parts of America suffer likewise from an 
unequal distribution of rainfall, and Professor 
Whitney of the U.S. Department of Agriculture, has 
for some years devoted his time to an examination 
of the moisture conditions which obtain in soils 
Although his work has already been productive cf 
most valuable and interesting information it is at 
present in Its infancy, and it is impossible to sav 
what this department of research may eventually ttll 
us. But some of the information gleaned la of 
great interest. 
In the first place, mechanical analyses of soils made 
by Whitney, Hilgard and others, have demonstrated 
that It consists largely of very minute particles, manv 
of them measuring only a few micro-millimetres in 
diameter, some indeed being even smaller than this 
or to put the statement popularly, they are little 
larger than bacteria. In loamy soils about one-half 
of the silicious matter consists of such material 
The result of this state of minute sub-division ia 
that It offers a very large surface, not only to the 
plant, to whom it is important, but also to the water' 
Perhaps will appreciate this if I say that each cubic 
foot of soil offers a surface area amounting to manv 
thousand square feet. One of the results of this 
13 that water is held, long after rain has ceased to 
fall, in very thin films on the surfaces of these small 
particles, and does not at onne evaporate into the 
air or run away as drainage water, as would be the 
case if the soil consisted of coarse pieces. 
Turning from the soil for a moment,' we may en- 
quire how much water an ordinary crop will reauira 
during its growth. This is a much larger amount 
than one might suppose. The results of the most 
recent investigations go to show that the quantitv 
varies from about 300 to 500 lb. of water per 1 lb of 
Ory crop. For example, m average good wheat croy 
