Feb. i, 192 1 Onion Smudge 699 



they occur in nature when spores are disseminated by meteoric water. 

 Diseased onions bearing spore masses were brought in and allowed to 

 dry out gradually in the laboratory, and the viability of the spores was 

 tested from time to time. Ordinarily a large percentage lost their 

 vitality within 2 weeks, but in some cases good germination occurred 

 after 7 weeks. A small percentage of conidia from spore masses pro- 

 duced on potato agar and exposed to similar conditions germinated after 

 4 months. Spores in water suspension allowed to dry out on glass 

 slides were very sensitive to desiccation, little or no germination occurring 

 after 24 hours. It is evident, then, that the conidia are sensitive to 

 desiccation except when they remain in waxy masses on the host, in 

 which condition a small percentage will remain viable through extended 

 unfavorable periods. These results are in accord with the findings of 

 Hasselbring (14) for the somewhat closely related fungus Gloeosporium 

 fructigenum, causing the bitter-rot of apple. 



On strom ata. — The stromata of the fungus are capable of withstand- 

 ing very long periods of desiccation. Test tube cultures of the fungus 

 on a large number of media were kept at room temperature for a period 

 of two years. Since the tubes were not plugged very tightly with cotton 

 the cultures dried out completely within four or five months. The 

 vitality of the fungus in this desiccated condition was tested by adding 

 sterile melted potato agar to the tube and slanting them until the fresh 

 medium hardened. Vigorous growth characteristic of the fungus re- 

 sulted from the cultures originally made on potato, beef broth, carrot, 

 corn meal, oatmeal, and onion agars, steamed rice and bean pods, and 

 fresh potato and onion plugs. The fungus was no longer viable on 

 synthetic agar, steamed potato, carrot, onion, and fresh carrot. Since 

 spores lose their vitality in such a long period of drying, it may be in- 

 ferred that the fungus lived through this extended period of desiccation 

 by means of the stromata which developed in the substrate. It is to be 

 expected from these results that the stromata which develop in the scales 

 of the host are capable of carrying the fungus over long periods of un- 

 favorable climatic conditions. 



EFFECT OF FREEZING 



On conidia. — Spores in water suspension exposed to freezing tem- 

 peratures are killed within a few hours. Fresh spore masses also are 

 very sensitive to low temperatures, but if they are allowed to dry out 

 before being exposed to freezing temperatures they will withstand such 

 temperatures for a month or more. In order to test the resistance of 

 conidia to the freezing weather of the entire winter period, infected 

 onion bulbs bearing spore masses were placed out of doors in a weather 

 instrument shelter at Madison, Wis., on December 7, 191 5. Germina- 

 tion tests showed a high percentage of these conidia to be viable at this 



