22 
make their appearance on the under side of the leaf, 
forming a powder — the so called “ rust ” — on the outer sur- 
face of the spot. Coloured drawings of coffee leaves thus 
affected with “disease-spots” were handed round for in- 
spection. 
As the number of yellow spots increase, the leaf loses its 
bright green colour, turns yellow, and drops off. As large 
numbers of leaves thus prematurely fall from the branches, 
the latter become shrivelled and brown, and the fruit drops 
in all stages. 
The lecturer then proceeded to describe the microscopic 
details of what is seen inside a healthy leaf, and compared 
it with what is found inside the yellow “ disease spots.” 
The passages between the green cells of the leaf are found 
to be blocked up by a fungus mycelium, consisting of short, 
much-branched tubes, which send off curious sucking organs 
into the cells. 
As the fungus grows older, and the yellow spots, which are 
the external evidence of its presence, become larger, it is 
discovered that the contents of the green cells become 
sucked out into the fungus. A section showing the my- 
celium and its minute sucking organs was shown under the 
microscope. 
When a section is taken through a more advanced spot, 
on which the yellow “ rust ” has formed, the origin of the 
latter is seen to be as follows : certain branches of the fun- 
gus grow together through the stomata of the leaf, and bud 
off thousands of spores. These numerous spores form the 
yellow powder or rust. An instructive section of this kind, 
in which the mycelium and spores were stained blue, was 
shown afterwards under the microscope. 
On one spot as many as 100,000 or more of such spores 
have been estimated, and 127 such spots were counted on 
one pair of leaves. They are detached with the slightest 
shake. 
