June 23, 1923 
Disease Resistance to Onion Smudge 
1033 
Yellow scale tissue: 
Undiluted.At 24 hours, a large percentage of ruptured germ tubes; at 
48 hours, no change. 
I to 2.At 24 hours, many ruptured germ tubes and many short, 
thick, germ tubes; at 48 hours, practically no change. 
I to 3.At 24 hours, short, thick germ tubes, no appressoria; at 48 
hours, good growth and appressorium formation. 
I to 5.At 24 hours, good growth and appressorium formation. 
Red scale tissue: 
Undiluted.At 24 hours, very little germination; when it occurred it 
resulted in ruptured germ tubes; at 48 hours, no change. 
1 to 2.At 24 hours, ruptured and short, thick, abnormal germ 
tubes; at 48 hours, some additional growth of latter. 
I to 3.At 24 hours, germ tubes slightly longer than in i to 2, no 
appressoria, an occasional ruptured germ tube; at 48 
hours, considerable additional growth, but no appres¬ 
soria. 
I to ^.At 24 hours, good germination and appressorium formation. 
It will be seen that in the undiluted extract of white scales, germina¬ 
tion was quite normal and compared favorably with that in onion decoc¬ 
tion. In the undiluted red and yellow scale extract “ruptured” germ 
tubes were common. As the colored extracts were diluted, however, 
there was a gradual diminution of the toxic effect with seemingly normal 
germination occurring in the i to 5 dilution This shows that the 
inhibition in the concentrated solutions was not due to a lack of nutrients. 
Moreover, the toxic entity was apparently about equally concentrated in 
the extract from the red and that from the yellow scales, if we may judge 
from the extent to which germination was reduced in equal dilutions of 
the two extracts. 
RELATION OF CELL SAP ACIDITY TO THE FUNGUS 
The reaction of the cell sap of the host plant as a factor in resistance to 
parasites has been emphasized by Comes (j, 4), but Jones, Giddings, and 
Lutman (10), Hawkins and Harvey (9), Vavilov (20), and others found 
no positive evidence of its importance as the cause of resistance. Since 
this point is not one to be overlooked, a study of the acid toleration of 
CoUetotrichum circinans was made. 
Onion decoction, a medium which had proved very favorable for germi¬ 
nation and growth, was used in this study. Two hundred gm. of fresh 
onion bulb tissue and 1,000 cc. of distilled water were cooked in the 
steamer for one hour. This decoction was then filtered through filter 
paper and the hydrogen-ion concentration of the filtrate determined. 
The medium was then divided among ten 200-cc. flasks and the acidity of 
each adjusted with standard solutions of hydrochloric acid or with sodium 
hydroxid so as to cover the following range of Ph values: 1.8, 2.0, 3.0, 3.6, 
4.4, 5.2, 6.4, 7.4, 8.8, and 9.4. A portion from each flask was used for 
spore germination tests and the remainder sterilized for 30 minutes at 
7 pounds pressure. The acidity of each flask was again tested after sterili¬ 
zation and the following values noted: 1.6, 1.8, 2.2, 3.4, 4.6, 5.2, 6.2, 6.8, 
7.4, and 8.2. Spore germination tests were also made with portions from 
these lots after sterilization. Good germination occurred in the alkaline 
media and in the acid up to Ph 3.4. When the acidity increased beyond 
that point, germination was reduced and abnormal. In the unsterilized 
extract at Ph 1.8 and 2.2, 10 to 15 per cent of the spores began to germi¬ 
nate, but the germ tubes appeared to rupture and exude cytoplasm in a 
manner strikingly similar to that observed in the water extract from dry 
