December i, 1881.] THE TROPICAL AGRICULTURIST. 
5i3 
easy to explain tl: 
spots and spores 
June. That such i 
doubt by the folio 
(1.) During the 
showed that the f 
many sporos to fa 
that somo of theso 
(2.) During the 
to see that ram 1 
runs down to the 
furrows to the edg 
formed often contai 
in this manner thai 
lal accumulation of disease- 
May and the first week hi 
planation seems placed beyond 
irtnight in May, observation 
of the branches had caused 
I10 leaves, &c, round about ; 
3d adherent cannot be doubted, 
nd May showers it was easy 
m the upper side of a leaf 
>f the leaf, or along natural 
J of EemiUia. It is evidently 
wash the spores to the edges 
3af ; once there, germination 
sphere remains moist for a 
spi 
lamination of the leaves in May showed that 
re present on the lower surfaces. Since the 
winas were not high, these probably reached their destina- 
tion in the manner described. 
(4.) I have shown that moisture, a proper temper- 
ature, and oxygen are alone necessary for geraiination, 
and that if this occurs on the lower surface of the 
leaf the tubes enter and form mycelia in tho intercell- 
ular spaces inside the loaf. An examination of the 
weather shows that just such conditions existed about 
the given periods as were required. 
As I have shown, spores were present in some quantity 
on the leaves before the end of May, and before the 15th 
of June the trees were becoming badly diseased. The 
last week in May was a wet one (after a fortnight or 
more of dry windy weather), and the atmosphere damp 
for some days; then again followed a short period of 
warm, steamy, cloudy weather with brighter intervals. 
That numerous spores were distributed in May, and germ- 
inated in the interval between May 25th and June 1st, 
there can be no doubt, and I have shown that if such 
was tho case, the resulting disease patches should begin 
to appear somo 15 days or so later. And this actually 
occurred; for on June 15th my notes run: — "All trees 
excopt tho one at south-west end badly diseased with 
I pin-spots," especially the lower branches. These lower 
branches arc sheltered and moist." 
It will thus be seen that the very close connection which 
exists between the parasite and its conditions of existence, 
: &c, can bo traced here, and it will also be seen that 
; this connection is no more mysterious than that between 
the life of any organism and its natmal environment: 
Bow tho spores of Hemileia on a proper nidus, and give 
i them air, water, and warmth, and they germinate and 
flourish as do the seeds of coffee or any similar plant in 
damp, warm, aerated soil. 
The stock of spores formed on the trees was already 
large, but after June 15th — 20th, an enormous increase 
occiutciI, and it is necessary to see the effect produced 
shortly afterwards. Tho weather on and about the 20th 
was hot and close, and every " disease patch " wus 
manufacturing thousands of spores, the mycelia being 
abundantly fed by the now well filled leaves; windy 
periods had also occurred, and, partly by shaking tho 
"rest" on to the samo or lower leaves, partly by rub- 
bing leaves together, and partly by carrying tho spores 
bodily through the air, the wind had caused a very eftcctu- 
al cussciuination of theso spores. Juno 2Gth to 29th 
were ncl dins, and thusr siictv- fullvdnoafcd spoivs v.iii. 1 
had not germinated already, no doubt did so now; at 
nervals, up to July 5th, wo had ulso wet weather. All 
•long were short periods of chiving high winds alternating 
with steady south-west breezes. 
It is clear that tho stock of spores accumulated from 
the disoase spots which commenced action on or about 
June 16th bad everything in their favour during the 
fallowing throe weeks, and it follows that during some 
three tvoeks later a corresponding amount of mycelium 
■hould be formed, and "leaf disease" be proportionally 
bad. The weather cleared up after July 5th and re- 
mained fine and hot for a fortnight or so, and during 
that pciiod a most disastrous outbreak of the orange- 
coloured rust occurred, especially during tho second week 
in July. These facts arc again closely in accordance with 
what should be expected from the experiments ; the disease 
spots which came out on July 14th, for instance, would 
be from spores which germinated about June 30th or a 
day or two before ; those which appeared on July 7th, 
from germinal tubes of June 21st or later, and 60 on. 
But still stronger evidence of these truths is afforde I 
by what followed. On or about July 12th the air had 
become quite dry again, and up to July 30th no rain 
fell ; from the 15th to the 30th, in fact, the ah- was so 
dry, and the winds (at intervals) so fresh, that probably 
no germination of spores could occur. Here, then, was 
a chance to test the accuracy of the preceding work, 
and I may mention that it was just such a dry interval 
that had before given me the clue to the facts. 
During these 15 days or so myriads of spores were 
formed and distributed by the wind. The rains came 
on again on August 1st, but the ah did not become 
very moist, and fine weather with dry winds intervened 
during the first week. The number of spores which 
would gei-minate successfully during this week would 
probably be few, because the air was probably at no time 
nearly saturated for 24 consecutive horns, and the leaves 
were never wet for anything like so long a period ; 
those spores which did germinate, however, should pro- 
duce visible disease-spots on or about August 15th to 
20th. I happen to have a curious and conclusive proof 
that such was the case. 
A perfectly clean and healthy plant of C'ojj'ea Arabica, 
which had been sent to me in a wardian case with three 
others from Samarang, Java, had been planted out 
direct from the case on August 1st amongst the badly 
diseased coffee ; it had been packed so that no injury 
accrued to it, and was altogether a satisfactory subject 
for experiment. I planted it in the evening of the day 
on which it was unpacked, shook a few spores from a 
neighbouring diseased plant on to one leaf, and moist- 
ened them with water ; rain fell during the night, and 
the next day was wet up to the evening, hence tho 
sowing was moist for about 24 hours at least. On 
August 18th there were one or two developing " disease- 
spots " quite visible to the naked eye, and on the 20th 
they were in full bearing. On August 7th, the rain 
commenced in earnest, and was of a character exactly 
suited for the germination of the spores — warm, steady, 
drizzling, continuing for hours, and saturating the air 
with moisture. Tins sort of weather continued to the 
12th, and two fine and still days followed ; then another 
wet period for a fortnight or so. The germination of 
the spores would be mainly effected between the 7th 
and 12th, however, and according to my previous results, 
a " bad attack of leaf disease " should be apparent 
about August 30th to September Gth. It is just hninin- 
ent, as I write this (September 2nd) there are pin- 
spots commencing to show on nearly every leaf.* 
§ 10. From the sequence of events thus occurring 
on a small mass of coffee, more or less under control, 
it is not difficult to infer what takes place on larger 
areas such as estates, or groups of estates ; but before 
examining this it is necessary to understand clearly a 
number of complicating circumstances. 
Certain portions of most estates are subject to con- 
ditions of a more extreme nature thun 1 have yet con- 
sidered. The ravines and hollows are in some cases 
never quite dry, and it becomes a serious question whe- 
• On September ilth, theso and numerous other disease- 
spots wore spreading all over, and before September 30th 
almost every leaf on tho above plant wus badly diseased. 
Tho three other plants, however, which had been placed 
in the N. K. verandah of my house, showed no trace of 
Heinileia up to October 7th! (the date on which I add 
this noto). 
