FLORIDA STATE HORTICULTURAL SOCIETY 
91 
The usual methods for investigating 
plant diseases were followed in studying 
this disease, but with little or no success. 
Melanose-infected leaves, twigs, and 
fruits were examined, but no fungus or 
bacterial organism was found associated 
with the diseased areas that could be con¬ 
sidered a cause of the trouble. Very thin 
sections of diseased spots were specially 
stained to bring out any fungous filaments 
or bacteria that might be present, but 
these gave negative results. Numerous 
cultures, under exact scientific control, 
were made, from diseased spots on leaves 
and fruit, in regular and special culture 
media, but we were unable to isolate any 
fungus or bacterial organism that we 
could suspect of being the cause. 
Attention was then directed to a study 
of the dead wood in citrus trees. It had 
been pointed out before that there seem¬ 
ed to be some relationship between the 
dead branches and twigs and the extent 
of Melanose infection. Observations in 
the groves confirmed this, for it was 
found that Melanose spotting was always 
heavier on fruit and foliage.immediately 
beneath dead branches. Some dead twigs 
were collected from orange trees badly 
spotted with Melanose. These were 
carefully examined with the microscope, 
and were found to contain a number of 
different fungi and bacteria. The Stem- 
End Rot fungus Phomopsis citri, was 
found more or less abundantly, but there 
was no special reason to suspect this fun¬ 
gus, for we knew it was the cause of one 
disease, and knew its customary habit of 
living in dead citrus wood. 
Experiments were then planned to see 
if it were possible to transfer infection 
from this dead wood to new orange 
growth. It was found that by suspend¬ 
ing a small bundle of dead twigs just over 
some young succulent orange shoots, and 
spraying this bundle with sterilized wa¬ 
ter, allowing the drippings to fall on the 
shoots, typical Melanose spotting could be 
produced if moisture conditions were 
controlled. Spots usually appeared as 
small sunken dots four or five days after 
treatment, and later developed into typi¬ 
cal Melanose markings. Small trees in 
pots were used in these experiments, and 
were so arranged that the foliage could be 
covered with a large bell-jar after treat¬ 
ment. Treated trees were kept under a 
bell-jar for usually twenty-four hours af¬ 
ter treatment. It was also found that 
washings made from these dead twigs 
when sprayed on young succulent growth 
would produce typical Melanose spotting. 
Spotting on new growth was produced in 
the grove, by tying dead twigs to young 
shoots, when sufficient moisture was pres¬ 
ent. 
These experiments proved that the 
cause of the spotting came from the dead 
wood, and whether it was some fungus, 
bacterium, or some toxic principle, was 
the next question to answer. Not being 
able to find any fungus or bacterial or¬ 
ganism associated with the diseased 
spots, we were led to suspect that there 
might be some poisonous principle in the 
dead wood that was responsible for the 
spotting. 
To clear up this point some other ex¬ 
periments were tried. It was found that 
washings from dead twigs when filtered 
to remove all fungus and bacteria present, 
would not produce Melanose spotting on 
