188 
C. M. Gibson. 
in autumn that I hunted the stems of the plants for a perennial 
mycelium, but found none. I then went and examined a collection 
which had been very badly attacked by the rust in the previous 
autumn, but which the gardener said was now quite clean. 
1, too, thought this to be the case for some time till one small 
pustule was discovered. There may of course have been one or 
two more, but even that one would be quite enough to account for 
an extensive outbreak when the plants were crowded together in a 
greenhouse. 
The histology of the fungus in its normal state was gone into, 
but shewed little of special interest, except the fact that the 
haustoria often contained several nuclei, up to as many as five. 
The chief interest centres round the fact that certain varieties 
of chrysanthemum do not take the rust, though growing in the 
midst of plants thickly covered with it. One such variety which, 
while growing with rusted companions, I had examined and found 
clean, was chosen to experiment upon. 
In the summer of last year leaves of this variety were inocu¬ 
lated with spores from a susceptible variety, and the inoculated 
spots were cut out and fixed each day, from the second to the tenth 
after inoculation. Sections of this material shewed that the germ- 
tubes had entered and had developed a mycelium with haustoria, 
just as in infection of a susceptible variety, though by the tenth day 
the mycelium was not as widely spread as in normal infection. 
The infected leaves which had been left on the plant did not 
develope uredospores; but by the fifteenth day (the normal period 
for the development of spores) the infected spots appeared as if 
corroded or scorched. These dead parts of the leaves on exami¬ 
nation shewed a further stage of the same destruction of the leaf 
by the fungus, as is described later in the case of the leaves 
inoculated in the following summer. 
The matter was at that time investigated no farther. In 
November inoculations were made on the leaves of flowering shoots, 
and nineteen days after inoculation uredospores appeared. A series 
of inoculations was then carried out, lasting till the end of March. 
These inoculations were made on flowering shoots, young shoots at 
the base of the plant, and on cuttings, but shewed no difference in 
result. Of thirteen sets of inoculations in all, uredospores developed 
in ten cases on some or all of the leaves inoculated; in the other 
three the inoculated parts of the leaves shewed the same scorched 
spots as in the Summer. The pustules which broke through were 
very small, but the uredospores were quite healthy and capable of 
