yoo Journal of Agricultural Research vol. xx,No. 9 



time. Tests made on January 22, 191 6, showed that by this date all 

 the spores had been killed. A similar experiment was carried out at 

 Madison in the winter of 1919-20. Infected bulbs bearing abundance 

 of spore masses were placed out of doors in October, 191 9, and protected 

 from rain and snow. A few viable spores were obtained on March 20, 

 1920. Thus, a few conidia may withstand Wisconsin winters if suffi- 

 ciently protected, but probably few, if any, live over under field condi- 

 tions. 



On sTromata. — Agar cultures containing abundant stromateoid de- 

 velopment were kept out of doors during the winter months at Madison, 

 Wis., during which period there was much severely cold weather. In 

 all cases the cultures were found to be viable at the end of this time. 

 Stromata on onion scales have also been exposed in this region during 

 the winter period, and in every case they withstood the severe freezing 

 temperatures. 



It is to be expected from the foregoing data that spore masses with- 

 stand short intervals of dry weather during the summer and furnish 

 ready inoculum upon the return of moist conditions. During extended 

 periods of unfavorable conditions, however, the stromata serve best to 

 perpetuate the fungus. 



PATHOGENICITY 



Inoculation experiments were performed on plants at various stages 

 of growth from young seedlings to mature bulbs. 



Sterilized greenhouse loam soil was inoculated by spraying with a 

 water suspension of spores at the time of sowing onion seed. Three 

 hundred seeds of White Globe variety were planted in the inoculated 

 soil and the same number in uninoculated soil. Ten days later, as the 

 cotyledons were coming through the soil, the attack of the fungus became 

 evident by the rapid collapse of the succulent tissue at any point on the 

 young shoot. Acervuli of the fungus were present and continued to 

 develop on the diseased portions of the plants. Fifteen days after 

 sewing, 64 out of 123 plants in the inoculated pot were diseased, whereas 

 all of the 161 plants in the control pot were healthy. This experiment 

 was repeated several times, and in each case where sterilized soil was 

 inoculated a high percentage of the seedlings were killed. When un- 

 sterilized greenhouse soil was used the injury was greatly reduced, 

 the competition of other soil organisms evidently greatly limiting the 

 activity of the smudge fungus. Moreover, damping off of this sort due 

 to smudge has never been noted in old onion set fields, other factors, 

 such as low temperature at this early part of the season, probably limit- 

 ing the activity of the fungus. 



Leaves of half -grown plants were sprayed with a spore suspension and 

 kept in a moist chamber for 24 to 48 hours. The fungus developed and 

 fruited on the lower leaves, which had reached a stage of "physiological 

 old age," but this never occurred on vigorously growing leaves. 



