92 
FLORIDA STATE HORTICULTURAL SOCIETY 
young growth. A part of the same wash¬ 
ings, filtered to remove only fungus 
spores and to allow bacteria to pass 
through, also failed to produce spotting on 
young shoots. Another part of the same 
washings not filtered, produced a heavy 
spotting on young shoots at the end of 
four or five days. 
These results indicated that Melanose 
spotting was not due to any toxin or 
poison in the dead wood, but more likely 
to some fungus. 
Repeated infection experiments were 
continued, using very small bits of dead 
twigs, less than a half inch in length. In¬ 
tense spotting was produced by some of 
these, and they were carefully examined 
under the microscope. It was discovered 
that Phomopsis citri was present on all 
these pieces, and in some cases was the 
only fungus present. 
Some experiments were then tried with 
this fungus. Spores from a pure culture 
were sprayed on young orange shoots, 
and in a few days typical Melanose spots 
developed on the leaves and stems. The 
experiment was repeated again and again 
with the same results. 
Some of the same cultures of Phomop* 
sis citri used by Professor Fawcett in his 
work on Stem-End Rot were used in 
these infection experiments, and all pro¬ 
duced typical Melanose spotting on young 
leaves and shoots. This established the 
identity of the cause of Melanose, but 
further experiments were carried on to 
make it more conclusive. Cultures of the 
fungus were obtained from various 
sources and grown in pure cultures until 
spores were produced. Some fruits 
were inoculated, and at the same time 
young growth was sprayed with spores 
in sterile water. The results from these 
experiments showed that spores from the 
same pure culture produced Melanose 
spotting on young shoots in four or five 
days, and typical cases of Stem-End Rot 
in sound, healthy oranges in seven to ten 
days after inoculation,. 
THE FUNGUS. 
In studying the habits of the fungus 
we find it lives chiefly in the dead wood 
of citrus trees, where it is carried over 
from one season to the next. Even in 
very small twigs countless numbers of 
fruiting bodies (pycnidia) mjay be found. 
These pycnidia are very minute, black, 
and imbedded in the bark, showing on the 
surface as small dark specks or small 
pustules. The interior of each pycnidium 
is a cavity connected with a small opening 
in the neck, which protrudes above the 
surface of the bark. Thousands of small, 
colorless, oval spores are produced within 
this cavity, and under favorable moisture 
conditions these are discharged through 
the opening in the neck in yellowish, 
sticky masses or tendrils. These spore 
masses are later dissolved by rain and 
dew and scattered about, producing infec¬ 
tion on leaves or fruit or new pycnidia 
in the dead twigs. The fungus is spread 
in the tree chiefly by rain and dew. 
Spores are washed from the dead wood 
onto leaves and from leaf to leaf until 
the entire new growth and fruits may 
become infected. 
The disease cannot be spread from the 
spots on leaves, twigs and fruits. Repeat¬ 
ed efforts were made to transfer the dis¬ 
ease from these spots to new growth, but 
without success. Infection is only caused 
by the spores and possibly the paraphyses, 
