Si4 
THE TROPICAL AGRICULTURIST. L Decemb e r i, 1881. 
ther the germination of spores is ever prevented in 
these places ; continual evaporation from the water below 
keeps the foliage of the cotiee moist, and, as such places 
generally possess very luxuriant and leafy trees, there is 
no lack of food for the fungus. The slightest shaking 
of the branches and leaves sheds spores around, and 
such hollows become quiet centres of disease, whence 
the wind periodically bursting in, further disseminates 
the spores. A similar argument applies in different 
degrees to flats where moisture is abundant from ex- 
cessive dews, &c. 
High and exposed ridges and faces are commonly 
badly diseased. This is partly because the wind con- 
veys spores very readily to such places, and partly on 
account of the damp mists commonly enveloping them, 
and affording the moisture necessary to germination. 
The fact that such regions are usually much washed, 
and therefore afford poor soil for the roots of the tree, 
has no more direct bearing on the subject of leaf -disease 
than has the converse fact that the soil in flats and 
hollows is usually good. 
Other things being equal, there can be no doubt that 
a gently sloping sheltered estate, or portion of an estate, 
suffers less than an exposed one, and if a dry climate 
is added to these advantages, the difference is even more 
obvious. On the other hand, an estate through which 
the wind blows freely, and the rainfall and general 
moisture of which is high, suffers more. The under- 
standing of these points is easy in the light of the other 
facts. 
§ 11. And now, bearing in mind what are the con- 
ditions which rule an " attack of leaf -disease," I will 
shortly examine one or two further illustrations, taken 
from both sides of the coffee country. 
My attention was drawn some months ago to a remark- 
able case of outbreak of Hemileia rust on a fine field 
of coffee situated in the following manner : — The whole 
estate lies in an incomplete basin, open to the east, 
and sheltered by high forest-clad hills on the west, 
south, and north sides. A steep ascent through jungle 
enables one to arrive at the top of the estate from 
the south-west side, and from this eminence one looks 
suddenly over the coffee on to the lowcountry beyond. 
The position of affairs was as foUows : the coffee to the 
extreme east of the estate alone suffered from " leaf- 
disease," and all the rest of the basin nestling under 
the forest-clad sheltering heights, had been free from 
"rust" until this year (this was in 1880). Could I 
explain the remarkable and sudden outburst of Hemileia 
on the south-west sheltered slopes? 
During 1879 and 1880 much of the jungle had been 
cleared on the other side of the ridge, and on riding 
up to the estate one felt the force of the wind severely. 
I have little doubt that the destruction of this shelter- 
ing jungle, which had hitherto prevented the carrying 
of spores (acting so to speak as a filter to the beating- 
wind), nuw enabled free passage of them, and the con- 
sequence was an outbreak of " rust " soon afterwards. 
Other instances of the same thing are not rare, and 
indeed we must look upon the opening up of such large 
unbroken areas of more or less well prepared food to 
the fungus as one of the chief causes of its lamentable 
abundance. 
On an estate in quite another part of the country, 
I found the natural featmes and then- effects illustrated 
in another manner ; the main fields of coffee lie on slopes 
chio-ily facing the east and north-east, and widely open 
in those directions to the low-country. Stretching up- 
wards, and much broken in character, lay coffee estates 
for several miles in a westerly direction ; the S. W. mon- 
soon sweeps all these estates before arriving at a broad 
plateau, or slight hollow which is situated at the top 
of the slopes referred to, and then, passing over the edge, 
falls down ihe^e slopes to the low-country. Now this 
plateau, notwithstanding that it possesses fine coffee, 
serves as a kind of reservoir of fungus spores, and for 
the following reasons ; the spores earned into it by the 
wind are very successful in obtaining a footing, since 
at that height there is usually sufficient moisture cling- 
ing about the coffee to enable them to germinate. Not 
only so, but every puff of wind sends spores produced 
hereon over the ledge to the slopes above referred to; 
these slopes are continually becoming infected, therefore, 
from above, and I have little doubt that were the pla- 
teau in forest instead of in coffee, these effects would 
cease to a corresponding extent. 
These examples may suffice to show how natural pecu- 
liarities of an estate affect its supply of disease-produc- 
ing spores ; but I would refer to other physical features, 
the action of which largely affect the question — in some 
cases masking, in others intensifying the ravages of the 
pest. 
The " lie of the land," as planters term it, is closely 
connected with this, since so many other things are 
' implied by it ; but it matters not how an estate is 
situated, so far as Hemileia is concerned, provided the 
spores obtain access to the coffee and moisture to germ- 
inate. An eastern aspect is often drier, less affected 
by wind, and, from these and other causes, possesses 
more luxuriant coffee than an estate facing the west; 
though in other cases the reverse holds good. But on 
going more closely into the matter, it occurs that a 
drier climate may mean less wash, and therefore better 
soil, which, of course, cceteris paribus, implies more 
luxuriant coffee ; again, absence of wind entails obvious 
advantages when one looks on the damage done to 
coffee torn by cold, boisterous blasts, while beating rains 
are well known to wash soil bodily away. 
Under such circumstances then, the natural advantages 
are all on the side of the coffee. Less Hemileia is 
blown into the place, and there is less continued moisture 
to favour its propagation, and therefore less chance of 
its spreading when once there ; while on the other hand, 
soluble and valuable constituents of the soil are more 
abundant, and the coffee is consequently more luxuriant, 
and shows the ravages of what disease there is less 
evidently. 
And this brings me to another and very important 
point. It is commonly stated that strong, thick, luxuri- 
ant coffee suffers less than poor, thin trees with few 
leaves, anfl it is asserted that this is because the weaker 
coffee is more " susceptible to the disease " than the 
luxuriant trees — that the latter possess some mysterious 
power of " throwing off the disease." Facts, however, 
are against any such view. 
A densely clothed tree, from the fact that it is not 
so easily penetrated by the wind, especially when sup- 
ported by a number of others, may not become so much 
" diseased " in a given time as a thinner one, every 
leaf of which is reached by the wind-blown spores. 
Again, the dense leathery texture of a strong leaf de- 
pends on its tougher cell walls, and repletion with 
food, sap, &c, hence the mycelium may not make such 
apparent havoc with the tissues of its leaves in a given 
time as it does in the thinner, softer leaf of the more 
unfortunate tree ; but there can be no doubt that the 
chief cause of the prevailing belief about luxuriant trees 
is that then- ability to produce foliage more rapidly and 
abundantly, partially masks the effects of the fungus 
by maintaining a general dark hue. 
The characters of the soil, again, are continually quoted 
as having a direct effect on the fungus ; but it will be 
seen from the above that, however much it may affect 
the coffee, good or bad soil only indirectly affects the 
fungus. It must be remembered that the mycelium of 
Hemileia requires living material, already manufactured 
by the plant, for its chief food. Of course, in so far 
as rich or poor soil enables the coffee tree to make 
this food, the mycelium present in the leaf is affected, 
and floiuishes well or ill. So with other peculiarities 
of soil, &o. A damp, ill-drained piece of land may 
afford an advantageous position for the fungus spores, 
inasmuch as they there germinate readily; but it is less 
so for the mycelium when once established, because the 
