28 BULLETIN 1474, U. S. DEPARTMENT OE AGRICULTURE 
true melanose markings they most likely developed from spores 
already on the leaves or from stray spores accidentally transferred 
with the mycelium, otherwise a larger percentage of leaves should 
have been affected. The water blank checks showed about as much 
infection as the inoculated plants. 
Inoculations with viable spores consistently failed to infect young 
leaves sprayed with lime-sulphur solution a few hours before the 
inoculum was applied. Similar inoculum heated to the boiling point 
failed to cause infection. Inoculum held for 24 hours at room tem- 
perature, 24° to 32° C. (75° to 90° F.), gave 100 per cent infection. 
In order to determine whether or not ordinary spring-bloom 
oranges and grapefruit can become infected with melanose during 
the late summer months, a simple test was made by tying small 
bundles of dead citrus twigs around the stems of fruit in August 
and leaving them there until the fruit matured. The dead twigs 
were especially selected for the presence of large numbers of fruit- 
ing bodies of the causal organism. No signs of infection had devel- 
oped on any of the -fruit by midwinter, when most of the grapefruit 
and some of the oranges were fully mature. 
Attempts were also made to infect living twigs at leaf scars with 
spores of the melanose fungus. Inoculations were made on twigs 
partially defoliated by applications of oil sprays as well as on twigs 
on which the usual natural defoliation had occurred. None of these 
inoculations gave the slightest indication of infection, nor could 
injury in any way be detected nine months later from the attempted 
inoculations. 
If such infections were to take place in nature there should be 
abundant and obvious indications of it, since some defoliation occurs 
regularly after applications of insecticidal oil sprays that are applied 
at almost any season of the year. In addition to this induced de- 
foliation, a fair amount of foliage drops each spring as the result 
of natural causes, but no evidence has been gathered to indicate that- 
such living twigs become infected and later die as a result of this 
infection. On the contrary, there is an abundance of evidence that 
twigs become infected after the bark has died from one cause or 
another. 
STJMMABY OF INOCULATIONS 
Summed up, the evidence at hand, together with the results of 
former investigators, prove beyond a reasonable doubt that melanose 
is caused by the fungus Phomopsis citri. The fruit and leaves of 
many rutaceous forms, including all citrus varieties grown commer- 
cially in Florida, are subject to attack by this fungus. Different 
maintained temperatures during the infection period and different 
lengths of exposure to the inoculum have a marked influence on the 
length of the inoculation period and on the degree of the resulting 
infection as well. Infection can take place in 12 hours at tempera- 
tures ranging from 15° to 30° C. (59° to 86° F.) ; the greatest degree 
of infection seems to occur between 20° and 25° C. (68° and 77° F.) : 
temperatures above and below 20° C. (68° F.) seem to prolong the 
incubation period. Attempts to infect hardened twigs through leaf 
scars failed. Likewise, negative results were obtained when leaves 
were inoculated with the mycelium of the melanose fungus. 
