CITRUS MELANOSE AND ITS CONTROL 
25 
ency was toward increasing the concentration of the inoculum. The 
thickness of the swab probably increased as time went on, permitting 
a slower drying out of the inoculum, which no doubt aided in accom- 
plishing infection. 
INOCULATIONS ON LEAVES 
In Table 3 it is shown that small leaves of the representative varie- 
ties of the orange, the grapefruit, the kid-glove oranges, and the 
lemon are at first very susceptible to melanose infection, and as they 
enlarge with age they become progressively resistant, reaching prac- 
tical immunity when they become about 2 inches wide, on an average. 
It is questionable whether the trace of " infection " that developed 
on these leaves was true melanose or some injury resulting from the 
wetted cotton swabs. 
Table 3. — Combined results of melanose inoculations on citrus leaves at Or- 
lando, Fla., 1919 to 1924 
Num- 
ber of 
varie- 
ties 
tested 
Width in 
sixteenths 
of an inch 
Num- 
ber of 
inocu- 
lations 
Per- 
centage 
positive 
Degree of 
infection 
Water blank 
checks 
Kind of citrus 
Num- 
ber 
Per- 
centage 
positive 
14 
11 
6 
6 
0to4 
5 to 8 
9 to 12 
13 to 16-— 
17 to 20.— 
21 to 24.... 
25 to 28. ... 
29to32.... 
. Over 32... 
0to4 
5 to 8. 
9 to 12 
13 to 16—- 
17 to 20— . 
21 to 24— 
25 to 28— . 
29 to 32.— 
Over 32... 
0to4 
5 to 8 
9 to 12 
13 to 16— 
17to20.— 
21 to 24... . 
25 to 28... . 
29 to 32— 
Over 32.. . 
0to4 
5to8 
9 to 12 
13 to 16— 
17 to 20— . 
21 to 24— 
25 to 28— 
29 to 32— 
.Over 32... 
384 
233 
407 
488 
462 
403 
238 
135 
157 
525 
124 
263 
386 
399 
445 
352 
251 
435 
256 
79 
149 
223 
139 
109 
60 
31 
7 
166 
82 
103 
136 
85 
56 
55 
48 
50 
91 
74 
65 
62 
49 
56 
24 
21 
10 
90 
70 
66 
73 
64 
48 
42 
31 
16 
94 
52 
37 
25 
22 
14 
15 
21 

89 
41 
54 
49 
48 
43 
38 
31 
24 
Severe 
do 
130 

do 
Medium 
do._ 
Slight 
Very slight.. 
Trace 
do 
Very severe . 
do 
""176" 
. 
Severe.. . . 
do 
do 
Slight 
Very slight. _ 
Trace 
do 
Very severe - 
Severe 
123 

do 
Medium 
3 

Kid-glove orange group 
Slight 
Very slight.. 
do 
Trace 
do 
Very severe . 
do 
64" 
. 
Medium ... 
Lemon 
do 
Slight 
Very slight __ 
Trace .. 
do. 
In addition to the inoculations listed in Table 3, numerous inocula- 
tions on leaves of various citrus and related plants, ranging from 
four-sixteenths to five-sixteenths of an inch in width, were also made. 
One hundred and seventy-four inoculations on five varieties of 
limes gave 91 per cent infection, averaging severe, whereas 75 water 
blank checks showed no signs of infection. 
In the sour-orange group 198 inoculations on five forms gave 82 
per cent infection that averaged severe in degree, and the 60 checks 
failed to become infected. 
