508 
THE TROPICAL AGRICULTURIST. [ December h 1881, 
After a stock of spores has commenced to accumulate, 
falling oft as they become ripe, and adhering to the leaf 
as the yellow or orange-coloured " rust powder," the 
completely exhausted leaf-cells, which have been de- 
stroyed by the mycelium, turn brown and decay, and in 
place of active, translucent, living cells, we find a mass 
of empty, shrivelled, useless, and discoloured vesicles. 
From what has been said above, it is evident that the 
resulting brown dead patch, seen from without, necessarily 
commences in the centre and spreads in a circular 
manner as before. Under certain circumstances, the 
second form of spore is produced later by the old spore- 
bearing heads, and shortly afterwards the growth ceases. 
In most cases, however, the attacked leaf falls before 
this, especially when many " disease spots" have be- 
come established in its tissues. 
The above is a short account of the succession of 
phenomena presented by the fungus on the coffee, from 
the germination of the papillate spore to the production 
of many similar spores from the adult mycelium ; and 
it must be noted that each one of these spores is cap- 
able of reproducing the same cycle of phenomena, pro- 
vided it meets with proper conditions of development. 
In this way the germination, growth, and reproduction 
of Remileia are repeated again and again on the coffee 
on estates. 
I will now proceed to state the results of observations 
and experiments made to determine the following points : — 
(a) What period is required ; and 
(6) What conditions are necessary, for the complete 
germination of the spore? 
(c) What length of time is occupied in forming a 
vigorous mycelium ? 
(d) How soon after the germination of the spore 
may the mycelium produce spores again ? and 
(e) How long may the " disease spot " luxuriate at 
the expense of the leaf? 
§ 2. («) How long a period is required, and (b) what 
conditions are necessary for the germination of the 
papillate spore ? 
I find that a spore of Hemileiais capable of germina- 
tion immediately after its complete formation on the 
diseased spot, and that in 12 to 24 hours after its removal 
from the " rust " patch to a healthy leaf, it may throw out 
its germinal tube : the conditions necessary for this are the 
presence of water oxygen, and a sufficiently high temperat- 
ure. If the mature spores be gathered dry and kept dry 
and cool for some time, no change occurs during that 
time ; nevetheless, spores thus kept for six weeks in 
a closely-stopped dry tube, germinated. In close covered 
cells, again, where the parts were sealed with wax, 
I have sometimes found germination delayed, or even 
altogether prevented. Finally, in cas'es where coffee on 
flats has become chilled or " frosted " by excessive 
radiation, the spores of Hemileia may be found de- 
stroyed in large numbers. 
The sum total of observations indicates that germina- 
tion occurs most rapidly in a warm, damp, steamy 
atmosphere on the surface of vigorous young leaves. 
Under these favourable ckcumstances, germination is com- 
monly completed and the tubes have begun to enter the 
stomata within 48 hours from the moment of sowing. 
Germination — i.e., the swelling of the spore, and pro- 
trusion of one or more germinal tubes — may apparently 
take place anywhere and on any surface, provided the 
necessary conditions of moisture, &c, are fulfilled ; and 
it is a fact that myriads of the spores germinate on 
substances other than a coffee leaf, only to shrivel up 
and die at the completion of the process.* Experiments 
already quoted in previous reports show that this is 
true for glass slips, and I have demonstrated the same 
for cloth, soil, and rocks on estates, &c. 
* There is, however, an exception to this statement, 
as I shall describe shortly, in the leaf of one other 
plant, Canthium ccvmpcmulatium. 
Where germination occurs on a living coffee-leaf, 
however, the tube does not thus die, but enters a stoma, 
and forms the mycelium as described above ; and this 
suggests the next question. 
§ 3 (c) What length of time is necessary for the 
formation of a vigorous mycelium? 
On the third or fourth day after a successful sowing 
of the spores, I almost invariably find a small branched 
mycelium within the leaf ; vertical sections of the in- 
fected part of the leaf show that the tube has pene- 
trated through the stoma, and begun to branch in the 
intercellular spaces connected with it, while horizontal 
sections of that portion of the leaf show that the 
branches (usually about three) at first spread in a 
direction parallel to the plane of the leaf. At first there 
are no haustoria, and the contents of the tubular, 
stumpy branches are pale and finely granular at the 
growing ends. 
Within a week from the date of entrance through the 
stoma, the mycelium has become a tolerably vigorous 
structure, rapidly spreading in a centrifugal manner as 
described, but still living on the fluids bathing the cells, 
the contents of which are still, to all appearance, healthy. 
During the second week the minute parasite increases 
rapidly hi size and vigour, and the leaf cells first attacked 
have by this time haustoria piercing then- walls in all 
directions, and, as a rule, sucking out then- contents. 
It is usually about the end of the second week, there- 
fore, before the pale discolouration (caused by the 
shining through of the damaged cells) first become 
observable. 
It will be seen further on how remarkably constant 
are the phenomena described ; nevertheless, it is not to 
be wondered at that some differences occur. It is of 
importance to note that no other conditions than those 
given appear to be necessary for the development of 
the mycelium. A succulent young leaf, with thin cell 
walls sometimes developes a spot more rapidly, probably 
because the cells are more easily emptied by the myce- 
lium than are those of an adult, leathery leaf, under 
the same circumstances ; but no evidence of a " necess- 
ary predisposition to disease " on the part of the coffee 
plant is forthcoming, and it cannot now be doubted 
that any leaf of any variety of coffee will allow of the 
entry of the tubes, and then- development into mycelia. 
So far as any general statement can be made on 
the subject, a vigorous and perfectly healthy leaf of 
West Indian coffee is quite as easily infected with the 
disease as an Eastern variety, or, if anything, more 
rapidly. 
No doubt the quantity and quality of food present in 
the leaf cells, the vigour of the sap-flow, the thickness 
of the cell walls to be broken into, and the number, 
&c, of cells to be attacked, have their due effect on 
the rapidity of development of the fungus ; and we 
already know that the degree of moisture, warmth, &c. 
as well as characters of soil, affect the coffee tree — and 
through it, of course, the parasitic fungus, is evident 
from the co-relations of both. It may be fairly stated, 
however, that under ordinary circumstances the pale, 
yellowish " pin-spot," heralding the outbreak of " rust," 
is observed about fourteen or fifteen days after germina- 
tion of the spore, and this is sufficiently constant 
(of course I speak from experience at Peradeniya) to 
enable one to predict the date of appearance of the 
disease spot, after making a sowing of the spores, 
with considerable certainty. 
To give an instance. On July 24th of this year a 
few yellow spores were sown on the under-side of a 
vigorous young leaf of a variety of Coffea arabica, and 
the sowing enclosed in a cell clipped on to the living 
leaf and kept moist as in previous experiments. From 
other experiments with the same variety of coffee dur. 
ing June and July, I was led to expect that the first 
indication of the yellow patch to the naked eye should \i 
appear in 15 days from the sowing of the spores, and \ 
