18 BULLETIN 1474, U. S. DEPABTMENT OF AGRICULTURE 
dead and weakened twigs and limbs were removed or whether rather 
heavy pruning was resorted to. 
Citrus melanose occurs on trees of all ages, but more freely in 8 to 
10 year old or older plantings. Even in bearing trees less than 10 or 
12 years old the disease is not likely to be of consequence if the trees 
have been kept in a vigorous condition, free of scale insects, and rela- 
tively free of deadwood. The damage done by melanose to trees of 
nonbearing age, including nursery stock, is of negligible importance 
except following freezes severe enough to produce an accumulation of 
deadwood or where dead pruning stubs above the buds have become 
sources of infection. 
Ordinarily melanose increases progressively with the advancing 
age of the planting, and in general those conditions which promote 
the accumulation of deadwood may be considered predisposing fac- 
tors to melanose development. 
When the leaf or twig is severely infected, complete defoliation of 
the twig occurs at about the time the leaf should normally develop 
the deep-green color of maturity. Twigs that bear these severely 
infected leaves are almost sure to die before it is time for the succeed- 
ing flush to come out, and those twigs that have died recently are 
sources of melanose infection later. Defoliation and blighting are 
usually worse on the inside of the tree than on the outside and invari- 
ably worse on the lower portions of the tree. 
MICROSCOPIC STUDIES OF MELANOSE MARKINGS 
Microscopic examinations of melanose markings have been made by 
Swingle and Webber (21), Floyd (10) v and Stevens (20) without 
finding consistent evidence of parasitic invaders. 
The writers also have made careful examinations of affected parts 
at intervals throughout the progress of this work. Free-hand and 
freezing microtome sections and paraffin sections, stained and treated 
in the usual manner, were studied. Examinations were made of old 
(pi. 3, A) and young lesions, and in addition especially careful ex- 
aminations were made of young leaf tissues of the kumquat, a very 
susceptible species, that had been in contact with spore suspensions of 
the causal organisms under good conditions for infection for 48 
hours, a sufficient length of time to produce melanose markings. 
The host tissue of recently inoculated parts gave pronounced evi- 
dence of having been killed for a depth of three or four cells, pre- 
sumably by the melanose fungus, but in none of the microscopic 
sections of young tissue was there evidence of fungal invasion. In 
some of the sections of old tissues there was very occasional evidence 
of fungal hyphee. This invader was possibly of a saprophytic 
nature. 
REISOLATION OF CAUSAL ORGANISM 
At intervals throughout the progress of this work on citrus mela- 
nose many systematic attempts were made to recover the causal 
organism from melanose blemishes. Both leaf and fruit tissues 
were cultured, and not only were old, rough melanose lesions used in 
these tests but also young, almost invisible spots and even inoculated 
parts that had not become visible. In some cases the surfaces of the 
affected parts were washed with common disinfecting agents, such 
