60 MASS. EXPERIMENT STATION BULLETIN 202. 



control of snapdragon rust that plants be dusted with powdered sulfur 

 every ten days, or sprayed with lime-sulfur 1 : 35. 



The wi-iter began his study of the toxicity of sulfur by testing the 

 toxicity of sulfur applied in water. Powdered sulfur, washed and freed 

 of sulfur dioxide, was added to drops of distilled water in which uredinio- 

 spores of P. Antirrhini were placed. These spores in water with sulfur 

 and the checks (spores in water without sulfur) were then placed at a 

 temperature of 10° C. Subsequent examination showed that the spores 

 in water with sulfur germinated quite as well as the spores in water with- 

 out sulfur. This result is not surprising, for sulfur, being insoluble, 

 would hardly be expected to have a fungicidal effect when apphed in 

 water. This result agrees with that of Melhus {loc. cit.), who found 

 that the spores of PhytophtJiora injestans germinated as easily in water 

 containing sulfur as in pure water. 



The toxicity of dry sulfur to urediniospores of P. Antirrhini was next 

 determined. Dry urediniospores were placed on slides and dusted with 

 powdered sulfur. These were then put into desiccators and kept for 

 three and one-half hours, some at a temperature of 12° C. and some at a 

 temperature of 21° C, then placed in drops of distilled water and set away 

 for twelve hours at their optimum temperature for germination, 10° C. 

 They were accompanied by unsulfured spores as checks. The following 

 table shows the relative germination of the spores sulfured at 12° C, and 

 those sulfured at 21° C. : — 



Table 11. Effect of Dry Sulfur and Temperature of Application on the 

 Germination of the Urediniospores. 



It is thus shown that spores dusted with powdered sulfur and kept 

 three and one-half hours at a temperature of 21° C. do not germinate. 

 Spores similarly treated, but kept during the sulfuring at a lower tem- 

 perature, 12° C, germinate as well as unsulfured spores. Sulfur at the 

 lower temperature is comparatively inert, but at the higher temperature 

 it reacts slowly with the oxygen of the air to form sulfur dioxide. 



The experiment just described shows that sulfur as such is not toxic 

 to the spores of this fungus. It is rather the sulfur dioxide generated 

 by the exposure of dry sulfur to warm air that is toxic to the spores of 

 the fungus. The more surface a substance exposes the more rapidly it 

 reacts chemically. Hence the necessity of having finely divided, that 

 is, finely powdered, sulfur rather than a coarser grade. 



