PLATE * 
Relation of volatile oil and scale pigment to the onion smudge organism. 
A. —Relation of outer colored scale to infection: Two bulbs of Yellow Globe (re¬ 
sistant) variety inoculated by placing drops of spore suspension, in onion decoction, 
at points indicated by black circles. 
Left: Inoculations made on diy, highly pigmented outer scale; no infection resulted. 
Right: The thin, dry, outer pigmented scales were removed from this bulb and the 
inoculations were made on the first fleshy scale, which contained relatively little 
pigment; scale infection resulted in a majority of cases. 
B. —Effect of volatile oil upon spore germination: Petri dish cultures prepared by 
pouring melted potato agar in which spores of the smudge organism were suspended. 
Plate at left exposed to volatile oil of onion ^ being inverted over a small amount 
of expressed onion juice for several days. The spores were all killed except ^ose 
around the outer edge of the plate. As the juice deteriorated due to bacterid con¬ 
tamination, growth progressed inward from the unaffected area. Plate at right 
untreated; normal germination and growth occurred thoroughout. 
