1036 
Journal of Agricultural Research 
Vol. XXIV, No. 12 
The possibility of a connection between acidity and toxicity in cold 
water extracts of dry outer scales was considered. Outer scales of red, 
yellow, and white bulbs were extracted for 24 hours in redistilled water 
having an approximately neutral reaction. For each gram of tissue 15 
cc. of water were used. The hydrogen-ion concentration of each extract 
was then determined and portions of each were used for spore germina¬ 
tion tests. The results are given in Table IX. Although the acidity of 
the outer scale extracts is somewhat higher than that of the succulent 
tissue, it was still in all cases within the range tolerated by the fungus, 
and the toxicity, therefore, must be due to something beside acidity. In 
none of these determinations was there any evidence of wide variation in 
acidity between resistant and susceptible bulbs. 
TabI/E IX .—Acidity of cold water extracts of dry outer scales of white and colored onions 
Variety. 
Ph value 
of extract. 
Reaction of spores. 
Ungermi- 
nated. 
Normal 
germina¬ 
tion. 
Ruptured 
germ 
tubes. 
Swollen 
spores. 
Short, 
abnormal 
germ 
tubes. 
Yellow Globe. 
Yellow Globe. 
Red Globe. 
White Globe. 
3- 70 
4.67 
3- 5S 
4- 03 
Per cent, 
52 
24 
91 
Percentaj 
numerc 
at 48 h( 
Per cent. 
0 
0 
0 
^e genninj 
jusappresj 
3urs, maki 
Per cent. 
47 
74 
8 
ition fairb 
;oria;new< 
ng spore c 
Per cent. 
I. 0 
I. 0 
0-5 
r high; goc 
:onidiabei 
lounts imj 
Per cent* 
0. 0 
I. 0 
0.5 
>d growth; 
ing formed 
>ossible. 
DISCUSSION OF RESULTS 
The resistance of the common colored varieties of onions to smudge is 
well established. The water extracts from the dry outer scales of red and 
of yellow onions have shown a marked toxicity to spores and mycelium 
of Colletotrichum circinans, and the reaction of the fungus is quite different 
from that brought about by the onion oil. In the scales of white varieties 
the toxic entity ordinarily associated with flavone or anthocyan pigments 
in the colored varieties, is apparently absent or too slight to be detected. 
Moreover, in the colored varieties, it is confined to dat tissue in which 
there has been production of pigment. Its absence in the unpigmented 
portions of the colored scales about the neck of the bulb is correlated 
with a marked susceptibility to the disease in this limited re^on. The 
fact that this toxic substance is readily diffusible in water indicates that 
meteoric or soil water immediately adjacent to colored bulbs may become 
sufficiently toxic to ward off invasion by the fungus. In any case, we 
are led strongly to suspect that by means of this toxic substance the 
dry outer scales of colored bulbs serve as a barrier between the parasite 
in the soil and the underlying fleshy scales, which have beep shown 
to be susceptible to infection. 
The exact identity of the toxic substance (or substances) remains to 
be determined. Its very close association with the scale pigments is 
suggestive. The toxicity may be due to the color compounds or to 
compounds closely associated with them. Attempts are now being 
made to isolate the substance in pure form, but it must be recognized 
