January 2, 1882.] 
THE TROPICAL AGRICULTURIST. 
649 
tho bushes at various heights, would it 1 e wise to 
gfgue that the boy who got most leeches attached to 
his 1)' dy was "more susceptible" or " specially pre- 
disposed " to them 1 
(3) I now pass on to consider the third statement, 
to which so much objection hns been raised, viz. : — 
" Manure cannot property be looked upon as a cure 
for the disease." If the organized materials or food- 
stuffs in the cells of the coffee leaf are the proper 
food of the parasite Hemileia, as is found to tie the 
case ; and if manure, after being worked up into 
organized materials, is a proper food for coffee, as no 
one will doubt it is, then it follows that iu manuring 
coffee to provide nourishment for the production of 
fruit, &c , we indirectly tpanure Hemileia. It should 
be remembered that the crop obtains its principal 
nutriment from the leaves, just as does the fungus ; 
and, unfortunately, they both take similar materials. 
It must be clear that we at least run a risk of 
increasing the amount of fungus and of iis spores (tiie 
orange-red rust), and therefore of the leaf-tissues beiug 
destroyed, &c, as we increase the amount of food-stuffs 
by manuring ; and if the fungus, i.e., the di» ascproduc, r 
is increased, it is obviously absurd to consider the dis- 
ease cured. I do not wish the above to be construed 
as meaning that manure should not be used in the 
cultivation of the coffee; it rnusl be used, or the 
drains ou the tree will be more than it can stand. 
It would be as rash to conclude that manure does 
no good to coffee suffering from loss of sap and func- 
tional disturbances induced by Hemileia, as to imagine 
that food could do no good to a man suffering from 
loss of blood, and certain consequences following it : 
in both cases, however, it should be borne in mind 
that the evil may be past remedy if the patient has 
been too long neglected. And it should also occur 
to all, that the prime cause of the loss of sap, &c, 
should be destroyed, by burning or burying all spore- 
laden leaves possible, by shelter, aud other precautions. 
Acoffeo tree badly afflicted with Hemileia aud bearing 
a la ,- ge crop suffers more than one bearing an equally 
largo crop but less fungus, or than one bearing more 
fungus and less crop — other things being nearly the 
same. It is known that both the fungus aud the 
crop drain the leaves of substances formed in their 
green cells exposed to light, air, &c, aud siuce by 
manuring we -upply crude sap (mineral aud other sub- 
stances in solution) in larger quantities to be worked 
up in the leaves, it is possible in a given case for a 
tree to support both crop and fungus until the former 
is all ripe, provided tho functional activity of the 
leaves &c was not already too far disturbed. 
It is now < asy to conceive the following possible cases: — 
(1) A treo isdelicient of manure and leaves, and suf- 
fers severely, because its tissues are not replaced nearly 
as fast a* tho fungus destroys them. (2) Sullicicnt 
manure is present to supply crude sap as required, 
and tho amount of leaf surface is large enough to 
provide food for all purposes; new leaves form as tho 
fungus destroys older ones, and the tree appears pretty 
eyeu throughout. (3) The tree is 10 richly fur- 
nished with leaves, and so abundantly provided with 
orudo sap, that the comparatively email amount of 
fungus mycelium is easily supported, and yet aim-d- 
ance of food materials remain for the tree, ns the 
leaf-cells elnborate what comes from tho rootn &c. 
Aud every degree of complication of these circumstances 
occurs, and ho who undertakes to explain tho con- 
dition of a tree must carefully bear this in mind. 
Not only do tre s differ in the number, sizes, density 
ftp., of their loaves, but they differ in the quantity 
of sporos which they receive. Not only do thoy dit- 
fer as to tho sources of incomo at the roots (clay, 
grub, water, "slab. rock" fto, have their different influ- 
ences) and from the leaves (their stoutness, number, 
exposure to Sunlight, moisture, wind 4o, have to DC 
es of 
red ; 
min- 
&c,) 
piss 
here 
considered); but they differ with respect to the nu 
and kind of drains on their resources (crop, Ieaf-1 
and mycelium, &c). It should not, therefore, be ri 
concluded that the differences which can be re 
explained by known agents are brought abou 
unknown causes: the wonder is not that two < 
trees should suffer unequally from "leafdbea 
it is ' rather that any one should expect otherwis 
hope that I have now shown why, in manuring disc 
coffee, without taking steps to remove the sourc 
reinfection as the leaf surface is increased, a se 
risk of increasing the amount of fungus is incur 
Day, that unless the conditions for spore ger 
ation happen to be witheld (rain, dew^ 
tho risk becomes a certain danger. I may now 
on to consider the last point with which we are 
concerned : 
(4) It is agreed fl at, while the coffee must be man- 
ured, to enable it to support crop etc., the sources of 
reinfection should be diminished, in order that all the 
food-products formed m the plant may go fur the 
benefit of the tree : how can the sources of re-infection 
be diminished ? On a small scale (as with coffee plants 
grown in wardian cases, lighted rooms etc. ) two ways 
are perfectly practicable. 
The spores of the fungus may be prevented from 
alighting on the leaves, or, if they do alight there, 
water can be withheld from them.andno disease appears: 
this is the first and surest method of preventing infec- 
tion. The second way is to kill the germinating fundus 
before its tubes enter the leaf and form the "disease 
spots": this method is less ceitain, because so many 
causes may co-operate to prevent the destruc' ive agent 
from seizing all the germinal fubr-s. Nevcrthefess, 
with care, this method is also successful. 
In the open air, however, and on large masses of 
coffee, under various kinds of control, the problem 
of destroying the spores becomes a much more dif- 
ficult one, since it is impossible to guard the tree 
eutirely from wind and moisture. Here also, how 
ever, both the above methods are available to a cert- 
ain extent. We may, first, devote our energies to 
the destruction of all spore-laden leaves and pranings, 
provide as much shelter as possible, and in every 
way seek to prevent spores from reaching the coffee, 
siuce, when once there, we cannot withhold moisture 
and prevent germination. Secondly we may devise 
some method of applying a destructive reagent to kill 
these spores which do reach ti e coffee. 
It is witM respect to the second method that so much 
has been written and attempted, and I will examine 
once more what the application of an external re- 
medy implies : 
1st. It must effectually kill all the germinal tube3 
before they enter the leaf (which they commence to do 
in about 24 hours from the b ginning of germination), 
and yet must not injure the coffee. 
These two iniportai t conditions further demand other 
properties on the part of the re-agent or " euro" 
employed, viz. : — (a) It must be capable of rapid and 
wide diffusi&h, so that it may extend into every cor- 
ner of the treee, and so reach the m-st remote 
spore, (b) It must be very soluble, so that ii may 
be takeu up by the water in which the germ-tubes 
are forming, (<) It must act for a long time, aid 
continuously, in order that the later germ-tubes may 
be attacked as they form. 
'2nd. But this is not all. Several ga-eous com- 
pounds can bo named which would satisfy the above 
conditions of effioaoy and safety, combined with pro- 
per) iei of diffkaibility, solubility, ho,, but most of 
thoni would bo too expensive. The reageuls to bo 
used on estates must b' very r/i'aj) in thu first in- 
stance, since large quantities will bo nrceesary. 
3rd. And the application of the rum dial aginta 
mutt be simple : tho plauter should be quite familiar 
