July i, 1881.] 
THE TROPICAL AGRICULTURIST. 
i3S 
the trees, for ia some cases the carbolic acid pene- 
trated in sufficient strength to collapse all tho cam- 
bium cells ; but this danger could have been easily 
iliminated hy weakening the strength of the applica- 
ion. 
2nd Set of Experiments : 
Instituted to determine with what success the 
fungus, in its more or less developed state, could be 
destroyed by external applications, choosing such sub- 
stances and chemicals as were known to be inimical 
to fungoid life. 
Out of the many substances tried (sulphate of iron 
and copper, arsenical solutions, acids, potash, etc. etc.) 
two chemicals were found, in our preliminary experi- 
ments at Doteloya, to have an eminently decided 
effect, both on the fully developed orange spores of 
the hemileia and on the yet unfruited mycelium, which 
both it killed without injuring the healthy tissue of 
the leaf. These two were sulphate of soda (10 per 
cent solution) and carbolic acid (1J per cent solution). 
Kither chemical in these solution changed the orange- 
coloured spores into whitish looking bodies consider- 
ably ehiuuk, appearing under the microscope as white 
empty shells, the unfruited u^celium dried up and 
left a brown spot as far as its ramifications extended. 
The observations were made under the microscope. 
Both these chemicals were tried on a practical scale 
by syringing their solutions through the foliage. The 
sulphnte of soda application was practically a failure, 
not more than ten per cent of the spots and spores 
being destroyed by it. The fungus Beems to possess 
a power of rofusing contact with it when applied as 
a spray, and this practical difficulty will probably 
occur with most saline solutions. 
Tiie application of carbolic acid guve more satisfactory 
results. Mr. James Blackett and Mr. Drummond, on 
close examination oftheareaa few days after the applica- 
tion, decided that from 40 to 50 per cent of the 
diseased patches aud spores of the fungus on the 
tjrees had been destroyed, without injuring the 
young shoots or leaves. But the practical difficulties 
of syringing a whole estate seemed insurmountable, 
and to quote from Mr. Blackett's appendix to my 
report on the results of these preliminary experiments : 
"the external application of the solution of sulphate of 
soda or the diluted carbolic acid have too many drawbacks 
in my [Mr. Blackett's] opiriion to make them at all 
practicable." 
Mr. Blackett laid more weight on the results of the 
let set of experiments, and I put aside therefore all 
consideration of topical applications, until I came to 
the conclusion that the results of the inoculation 
piocess with carbolic acid were not sufficiently good 
to enable us to battle with the disease with any chance 
of success. 
1 then once more considered carefully the subject 
of external applications, the practical difficulties of 
applying liquids etc., and finally decided to try carb- 
olic acid absorbed into and used as dry powder in the 
same manner as sulphur and lime, as an external 
application. 1 used this powder, consisting mainly of 
finely slaked and sifted coral lime, in a strength of 
about \\% per cent acid. 
Though the carbolic acid is essentially an alcohol, 
it enters into a feeble combination with caustic lime, 
and forms what may, though somewhat incoirectly, be 
sailed a oarbolate of lime. 
On ex .osuro to the atmosphere the carbonic acid 
thereof combines with the lime, sets the carbolic 
iridfree, which thus escapes as vapour into the atmo- 
sphere. 
Used in this way, tho carbolic acid powder has given 
mo such satisfactory results that I have had no reason 
yet to obange either its strength or tin- mode of applica- 
tion. The treatment of a diseased arei with this powder 
cast broadly through tho foliage of the trees results 
iu stems, branches, leaves, and every square inch of 
ground being covered with an appreciable layer of the 
powder. The ground, stems and branches are covered 
most thoroughly, but a portion of the lower surface 
of the leaves seems to the naked eye always to have 
escaped somewhat the application, though underamagni- 
tyi»g glass, the fine, impalpable particles of the pow- 
der can even there be seen in multitudes. 
The effect of the treatment on the disease is: 
1st the destruction of spores and other forme of 
the fungus on the ground, 2nd destruction of 
spores on fallen leaves, on the stem and branches 
3rd destruction of spore patches on the foliage 
of the lower branches and the drying up and prevention 
of fructification of the pinspots on the same ; and 4th 
the partial destruction of spores and drying up of 
pinspots on the diseased foliage of l he higher branches. 
Bearing in mind I he great importance that hns been 
laid by Messrs Abbay, Ward, and others, on the 
gathering and burning of the diseased leaves which only 
represent a small fraction of the spores that have 
been shed in any one area, the benefit derivable from 
a wholesale destruction of not only the sports on th« 
fallen leaves but also of those that have fallen on 
the ground and the majority of others distributed 
elsewhere in the treated area will, no doubt, be fully 
appreciated. 
The treatment will have a maximum destructive effect 
on the different forms of this fungus on the ground, 
on the foliage of the lower branches, in the absence 
of high winds and in coffee which covers the ground 
well and when there are heavy dews or a slight shower 
after the application to supply the moisture necessary 
for contact. I have not yet finally decided 
whether heavy rain immediate/!/ after the application 
neutralizes the benefit. Heavy rain a day or two after- 
wards does not. Under favourable circumstances, pinspots 
and spores.even on the highest branches, w ill be affected 
by the vapour being retained within the area. It will, 
on the contrary, have a minimum destructive effect 
during high winds, on badly covered ground, open 
patchy places, on trees bordering the upper side of 
road etc, 
The vapour of the carbolic acid in an area thus 
treated under average favourable circumstances is dis- 
tinctly noticeable by iis penetrating smell for about 
eight to ten days after application; and in addition to 
the destruction of countless numbers of spores on the 
ground and on the fallen leaves by the 3| per cent 
carbolic acid powder, there has been unmistakable 
evidence collected that so long as the atmospheric air 
is tainted with the vnpour of this mo-t powerfully 
antiseptic chemical, the disease can make no progress. 
The catholic acid vapour is, of course, during this 
period breathed and absorbed into the system of 
the tree by the stomata of the leaf, and its effect 
of reducing the susceptibility of the tree to the 
disease is very much the same, and rests on the 
same basis as the effect of the inoculation process 
with the same chemical, and which already has been 
fully explained. 
It will now be easily understood that if an estate is 
dosed in a proper manner, and at a proper time, 
with this carbolic acid powder, it may be carried 
through the period of an attack with little appreci- 
able damage. 
I have since March last now treated over 800 ores 
of coffee with i his method of vaporiz it ion; have also can ■ 
fully, from time to time, examined wl at had been 
done iu January last, as well as what of the large 
area had been done first, and have now filially 
como to the conclusion that by two nppliea : ions costing 
R4 to R5 each per acre, used at a proper time 
I and under average favourable circumstances, an estate . 
I can bo carried through an attack >•( the disease with 
I little damage, and that the dimiiiishmout of spores (when 
operations arc earned on over a consult aide :nv,| 
and the general improvement in the tone of tin trees 
