December i, 1881.] THE TROPICAL AGRICULTURIST. 509 
accordingly made a note to tlie effect that the " pin- 
Bpot" should be visible on August 8th, following. 
The plant was put into a closed wardian case, and 
remained quiet as in other experiments. 
On August 7th, the first indication of a barely visible 
yellowish discolouration was detected; this increased 
more or less succe; 
id call your attenti 
to the following fa< 
further beyond cavi 
The fungus rnycel 
covered by the area 
no matter how " vi 
the early discolourc 
leaf or plant. I ha 
a case, each of vv 
In each example tl 
region of infection 
other spot ha 
elsewhere on 
few examples out ol 
tho samo thing. Wi 
question. 
§ 4. (d) How soi 
the 
germination of the 
pores again? 
snd upon experiments 
quoted, and the out- 
few spores generally 
v patch a day or two 
eye — i.e., during the 
in commences to bear 
of tho same nature as those 
como of theso indicates tl 
appeal- in the centre of the 
after it is visible to tho u 
third week of its life tho n 
tho spores in the manner described above. There ap- 
pears to bo more variation in the tune required for the 
production of spores, however, than in that required for 
the formation of the mycelium. In very hot weather 
after rain the rapidity of their formation is marvellous, 
and tho yellow patch is quickly covered with the 
orange-coloured dust. They, moreover, are produced more 
rapidly and iu greater quantity on a vigorously active 
young leaf than on an old matured one under the same 
conditions. That the nutrition of the leaf-cells, by 
aftecting that of tho mycolium, influences the amount 
and rate of development of spores, there can be no doubt ; 
and cases are not uncommon where the mycelium produces 
no spores at all, or very few, and these very slowly. On the 
other hand, iu very succulent, quickly-grown leaves with 
Bis-walled tissues, and full of fluid, I have known the 
spores to appear in 10 days from the sowing of the original 
Roses, mid lam informed by Captain Boyley of Gallo that 
he has found a sucker which was not 14 days old, with the 
spores fully developed upon tho leaf. This would also ap- 
pear to be a case in point. Nevertheless, in the majority of 
experiments tho spores appeal- during the third week— a 
result which, as already stated, admits of prediction being 
bonded upon it with considerable accuracy. 
As to the number of spores produced, and the time during 
Which tho mycelium produces them, no general statement 
can be made. As already said, no spores at all appear in 
Bomo coses, while on well- nourished mycelia their numbers 
ore enormous. In some of my experiments, where only one 
poteli of mycelium is fed by the plant, 1 have noticed long, 
Mndent clusters of spores hanging down from each stoma 
into Hi" perfectly quiet atmosphere of the wardian case. 
) Supposing each of these clusters to be l-25th of an inch 
long, and that 100 of the clusters depend from the wholo 
I patch, it may be deduced, from certain known particulars as 
] to tho size, Ac., of the individual spore, that in the example 
given then were probably a hundred and fifty thousand 
' yom visible at the tame time. ThiB was on one rust patch, 
| and I have counted as many ns 127 disease spots on a 
sinjjlc pair of loaves. 
. Of course, such pendent olostcrs never form in thi open, 
■inco the slightest movement of the leaf by currents of air 
128 
would scatter the loosely-attached spores in all directions : 
nevertheless, equal numbers must be formed on estates, 
only the wind detaches them as fast as they aie matured. 
A simple proof of tho successive appearance of the spores is 
afforded by the following experiment. On lightly rubbing 
the end of tho finger or a brush over a rust patch, vigor- 
ously active in fine weather, all the spores may be removed 
from the spore heads except very rudimentary ones : on re- 
examiiiing the smooth patch some 21 to 18 hours after, the 
powdeiy spores have again covered the patch. This may 
even occur on the ground, so long as the leaf still retains 
its green colour — a fact of no small importance in consider- 
ing the possibility of removing fallen leaves. 
§ 5 (e). — As to tho time during which the above spore- 
production goes on, I have established the following facts. 
In experiments where only one disease spot is allowed to 
flourish on a single leaf of the plant, the spores may be 
formed continuously during eight to ten weeks or longer if 
the plant is in a vigorous state and kept undisturbed : even 
in the open, I have watched disease-spots on which spores 
continuously appeared for five or six weeks in fine growing 
But, as a rule, the leaf falls before the mycelium has 
attained the possible limits of its development, either from 
being torn off by wind, or because numerous " disease 
spots" have formed, and the leaf soon succumbs to the 
multitudinous drains on its resources. It is certainly a 
remarkable fact that a leaf will support one or two " dis- 
ease spots" for a long time without apparent injury ; but 
this is easily explained if one bears in mind that the 
limits of the mycelium closely correspond with those of the 
discoloured-patch. Excepting that a tax is put upon the 
cells in more distant parts of the leaf — since the local action 
of the mycelium is very powerful — it must be remembered 
that all the green parts of the leaf are still practically 
healthy, and can do work for the plant. In proof of this I 
may cite an experiment made on a healthy plant of Jamaica 
coffee. Tho leaves were aU removed but two, besides the 
terminal bud ; a sowing was made on one of the two dark 
green, full-sized, and very fine leaves. On January the 
28th the first spores arose from the yellow " disease spot," 
increased in numbers, and were produced in abundance 
during the following two months. The activity of spore 
production then slowly dimiinshed as the destroyed tissues 
turned black, but up to May 25th, (i. e. nearly four months 
later) there was stili a feeble production of spores around 
the edges of the slowly spreading spot ; the rest of the leaf 
remained dark green, and, to all appearance, perfectly 
healthy ; and so it has remained up to this date (October 
5th)— half the leaf black and shrivelled from the action of 
ol now ones have 
e several "disease 
jwever, the latter 
jeeurs on estates 
been formed by the plant. In cas 
spots" aro permitted to drain tho 
soon falls, and this is of course 
generally. 
The Life-history of a pair of Coffee, leaves, before and 
after being attacked by HemUeia. 
I will now trace tho history of a pair of leaves, as actually 
observed on coffee in the open, as a simple example of 
what occurs where the conditions cannot bo controlled as 
in tho above experiments. 
§ 6. The bud, a terminal one, becamo exposed about the 
1st of March, 1881, as the then end pair of young leaves 
diverged from one another ; it remained as a minute green 
point, shining and hard from the resinous coating excreted 
over it, up to March 14th. Soon after, about March 21st, 
a gradual swelling of the bud was observed, and by March 
2'Jth, the two new leaves were seen us dork green, some- 
what ovate bodies, tightly oppressed face to face, and about 
a quarter of on inch long. 
If wo now examine the kind of wmther which, generally 
sneaking, prevailed during this period, a natural corre- 
spondence is traced between it and the development of tho 
bud. During the first three weeks of March, o continuance 
