Nov. 15, 1924 
Union Scale Pigmentation 
509 
Table I. —The effect of water extracts from dry outer scales of White, Yellow, and 
Red Globe varieties of onion on the germination and growth of several species of 
Fusarium as compared with Colletotrichum circinans 
Organism 
Experi¬ 
ment 
No. 
Germination in— 
Length of germ tubes in— 
Con¬ 
trol 
White 
scale 
extract 
Y ellow 
scale 
extract 
Red 
scale 
extract 
Con¬ 
trol 
White 
scale 
extract 
Yellow 
scale 
extract 
Red 
scale 
extract 
Colletotrichum circinans... .. 
Fusarium cepae. ... 
F. sp. 45_ 
F . lycopersici... ... 
F. graminearum.. .. 
{ i 
{ i 
i 
Per cent 
99 
95 
87 
100 
50 
99 
95 
Per cent 
80 
95 
98 
95 
50 
56 
95 
Per cent 
0 
0 
8 
23 
1 
0 
1 
Per cent 
2 
Microns 
414 
Microns 
224 
Microns 
0 
Microns 
0 
6 
582 J 368 
134 
17 
0 
1 
0 
96 ; 36 
0 
i 
tion of dry, outer, yellow or red scale 
tissue, however, resulted in a general 
reduction of germination or incom¬ 
plete inhibition. The effects are quite 
as marked as earlier noted for Colleto¬ 
trichum circinans. The growth of the 
germ tubes is somewhat reduced by 
the addition of white tissue in the 
case of both Fusarium cepae and Col¬ 
letotrichum circinans. With Fusarium 
cepae, where some germination occurred 
in colored scale extract, marked retard¬ 
ation of growth is evident. As found 
with Colletotrichum circinans, no strik¬ 
ing difference in the comparative tox¬ 
icity of extracts from red and yellow 
scales was noted. 
The data show that onion Fusaria 
are distinctly inhibited when sub¬ 
jected in this way to water extracts 
from dry, outer, colored scales. From 
the tests with two other species of 
Fusarium it may be expected that the 
toxins are equally effective upon forms 
other than those parasitic on onion 
bulbs. Should these organisms nor¬ 
mally invade the bulb through the 
outer scales we might expect a differ¬ 
ence between white and colored varie¬ 
ties in susceptibility, as generally noted 
for onion smudge. Since, however, 
the onion Fusaria normally invade 
through wounds or possibly through 
natural openings in the stem plate (7), 
the possibility of the scale toxins com¬ 
ing into immediate contact with the 
invading parasite is very slight. Con¬ 
sequently, little or no evidence of 
resistance to Fusarium bulb rot can be 
expected among colored varieties, and 
this supposition is confirmed by the 
writers’ studies so far. In another 
paper (7) a field experiment is reported 
wherein plantings of several varieties 
of onion, including the three color 
types, were artificially inoculated with 
Fusarium cepae. Infection results at 
the end of the season were as follows: 
Percentage of fusarium bulb rot 
Variety: 
Red Globe_ 12 
Yellow Globe_ 8 
White Globe_ 18 
White Portugal_ 8 
There is therefore no marked indi¬ 
cation of varietal resistance between 
the colored and white varieties in this 
instance. Further study on this point 
is needed. 
RELATION OF PIGMENT TO DEVEL¬ 
OPMENT OF CERTAIN SPECIES 
OF ASPERGILLUS AND HELMIN- 
THOSPORIUM 
Aspergillus niger is found commonly 
after harvest on the outer scales of 
onion bulbs, where it develops largely 
as a saprophyte under sufficiently 
moist conditions. Aggressive invasion 
of the fleshy scales is seldom if ever 
to be found. Although perhaps some¬ 
what more common and conspicuous 
on white varieties, the colored forms 
are often affected as well. Aspergillus 
sp. 4660 was isolated from decaying 
garlic bulbs and by inoculation experi¬ 
ments has been shown to be an active 
parasite of the succulent scales of onion. 
The data in Table II show that 
neither of these forms is inhibited by 
outer white scale extract. In the case 
of Aspergillus sp. 4660, germination 
was always better in the white scale 
extract than in the control; as a rule 
it was either decidedly retarded or 
entirely inhibited in the colored scale 
extracts. Likewise, growth in the 
white scale extract was about equal 
to that in .the control, or better, while 
in the colored scale extracts it was 
decidedly retarded. In one experiment 
with A. niger, germination was in¬ 
hibited by yellow scale extract and 
much reduced by the red scale ex- 
