Feb. i, 1921 



Onion Smudge 



701 



The disease was produced many times by means of artificial inoculation 

 of healthy mature onion bulbs with suspensions of spores from pure 

 cultures, and the fungus was readily reisolated. A summary of these 

 inoculations is given in Table II. In certain cases when bulbs kept in a 

 closed chamber were thus inoculated, the experiment was unsuccessful. 

 It was found in such instances that although the spores were capable of 

 germination in water, they did not germinate in the drops on the bulbs. 

 The inhibitive effect of the volatile oil of onion on spore germination 

 was mentioned eailier by the writer (38). An accumulation cf this 

 substance when several onion bulbs are placed in the small space in a 

 moist chamber may possibly account for this lack of germination. 

 Further studies on this point will be described in a later paper. 



More nearly uniform results were secured when sterilized soil was inocu- 

 lated by spraying with a spore suspension and healthy bulbs then inserted 

 in this medium for a week or 10 days. The outer scales usually became 

 uniformly infected in 7 or 8 days (see Pi. 81, C). When the bulbs were 

 removed and placed in storage, typical invasion of the underlying scales 

 occurred. 



Table II. — Summary of inoculation and greenhouse experiments on onion bulbs 



Type of inoculation. 



Date of in- 

 oculation. 



In soil 



Dec. 3 

 Nov. 30 

 Dec. 16 



Method of 

 inoculation. 



Sprav 

 .do 

 .do 

 .do 

 .do 

 .do 

 .do 

 .do 

 .do 

 .do 



Inoculated. 



Num- 

 ber of 

 onions 

 used. 



Percent- 

 age in- 

 fected. 



IOO 



IOO 



IOO 



80 



o 



IOO 

 IOO 



IOO 

 IOO 

 IOO 

 IOO 

 IOO 



Num- 

 ber of 



days 

 before 



first 

 note of 

 disease 



Controls. 



Num- 

 ber of 

 onions 

 used. 



Per- 

 cent- 

 age in- 

 fected 



In general, then, the fungus assumes the role of a weak parasite. 

 Actively growing portions of the plant are not attacked except in young 

 seedlings grown under certain conditions. In the field the fungus is 

 confined to the outer leaves or scales, the cells of which are dead or essen- 

 tially functionless. As the plant approaches maturity the dry outer 

 scales of the bulb are invaded, but the normal fleshy scales are not 

 affected at this time. A few cases have been noted where the fungus 



