1922] 



YOUNG — THE TOXIC PROPERTY OF SULPHUR 407 



Gimingham, and Wiltshire ('20) concluded that calcium thio- 

 sulphate, hydrogen sulphide, and sulphur dioxide were all slight- 

 toxic but not sufficiently so to account for the fungicidal 

 value of lime sulphur. The calcium pentasulphides were toxic, 

 but since they disappeared in a few hours the lasting toxicity of 

 lime sulphur could not be attributed to them. They concluded 

 that the lasting toxic property must be due to precipitated sul- 

 phur. Doran ('22) also found that the sulphides decomposed 

 very rapidly, especially when dried slowly. 



Several other sulphide preparations have been employed as 

 fungicides but have proved more or less ineffective as a lasting 

 spray because their retention on the tree as sulphides is difficult 

 to maintain. Their caustic nature frequently results in severe 

 burning. 



In testing the toxicity of sulphur and its compounds consider- 

 able confusion has developed owing to the variation in resistance 

 of different species of fungi. Barker, Gimingham, and Wiltshire 

 ('20) found that germination of the spores of Sclerotinia jructi- 

 gena and Phragmidium subcorticium were entirely inhibited in 



a suspension of flowers of sulphur in Van Tieghem cells. Ger- 

 mination of Fusicladium dendriticum and Cladosporium julvum 

 were 50 per cent inhibited, while that of Nectria ditissima, Bo- 

 trytis cinerea, and Verticillium sp. was not at all inhibited. When 

 the flowers of sulphur was used Doran ('22) found that a much 

 higher temperature was necessary for the killing of spores of 

 Botrytis cinerea than for Venturia inaequalis and a higher tem- 

 perature for the latter than for spores of Sclerotinia cinerea. 



Experimental 



Since most of the evidence listed in the foregoing references 

 points to sulphur as being the toxic agent regardless of the sul- 

 phur mixtures used, it was first thought important to study the 

 influence of the sulphur particle and molecule on the germina- 

 tion of spores. The Van Tieghem cell and the hanging-drop 

 culture method, later slightly modified, were employed. The 

 percentage of germination of the spores was used as an indication 

 of toxicity. The organisms used were selected from the group of 

 strict parasites most of which are of economic importance. It was 

 also necessary to select those that sporulated readily. The fol- 

 lowing forms were used: Colletotrichum Gossypii, Sclerotinia 

 cinerea, Botrytis cinerea, Glomerella cingulata, Gloeosporium 



