23 
Mr. Ward then described the germination of the spore. 
On glass or inorganic bodies the spore, after a few hours in 
water, throws out a tube, which reaches a certain stage in 
24 — 48 hours, and then dies. In nutritive fluids of various 
kinds, also, or on the upper side of the leaf, stem, &c., no 
further development was possible. On germinating the 
spore in drops of water on the under side of the leaf, how- 
ever, the germinal tube soon enters a stoma , and at once com- 
mences to form the mycelium inside the leaf. This grows, 
feeds on the cell contents, blocks up the passages, &c., and 
causes the development of a yellow “ disease spot,” such as 
those described. 
Experiments were made which showed that the yellow 
disease spot only appears where such a tube has entered the 
leaf, and nowhere else on the leaf or plant, and that leaves 
or plants on which no spores were sown — and therefore no 
tubes entered — formed no spots. Shelter from spores is a 
certain guard against disease. 
It was found, as a mean of very many experiments, that 
the yellow disease spot appears about 14 days after the 
sowing and germination of the spore on the leaf, and that 
the spores constituting the “ rust ” of such a spot commenced 
to form during the third week after the sowing. 
The yellow disease spot, therefore, is the outward appear- 
ance produced by the fungus mycelium occupying the space 
in the leaf. This mycelium blocks up the passages, robs the 
cells of food substances which should have gone down to 
the branches, fruit, &c., interferes with normal respiration 
and other processes, and thus shortens the life of the leaf. 
Since the tree thus derives so little benefit from its leaves, 
it cannot bear so much fruit. 
Further experiments proved that the age and condition of 
the leaf, the kind of coffee, &c., have no effect on the pro- 
blem of its infection ; all can be infected, though thick leaves 
can support more mycelium than thin and succulent ones. 
