86 



James G. Horsfall 



Bank's colloidal sulfur dust prevented germination completely at all 

 temperatures and hence is not included in the table. The differences in 

 germination in Kolodust were not great at any temperature. The same 

 is true of the germination in 300-mesh dusting sulfur, but the latter 

 invariably allowed more germination than the former. 



It appears that sulfur is as active at one temperature as at another. 

 Kolodust shows less variability in this respect than does 300-mesh dusting 

 sulfur. This is probably due to the fact that the 300-mesh sulfur is near 

 the border line of toxicity. It has been pointed out previously that dusts 

 at the lower limit of toxicity cause variations in germination in different 

 experiments because of difficulties inherent in the method of application 

 of the dusts. 



Caution must be observed in drawing conclusions from the data. One 

 could not say, for example, that sulfur does not kill by volatilizing, but, 

 if volatilization is responsible, it proceeds sufficiently rapidly at 3° C. to 

 inhibit the germination of Heterosporium phlei, and that an increase in 

 temperature from 3° C. to 25° C. does not change the degree of toxicity. 



If all the germinations in the checks and in the two sulfurs be considered 

 as accurate indications of their true values, then a summary of the results 

 with sulfur is obtained as shown in table 24. 



It is readily evident from the table that Kolodust is superior to 300- 

 mesh dusting sulfur in efficiency, but that both are rather effective in 



TABLE 24. 



Summary of the Effect of Sulfur on Conidial Germination of 

 Heterosporium Phlei 



Check, E,„ = 91.6 ± 0.76. 



Kolodust, E, n = 9.56 ± 0.046. 



300-mesh dusting sulfur, Em = 26 . 6 ± 2 . 84. 



