1922] 



YOUNG THE TOXIC PROPERTY OF SULPHUR 421 





The results in this table are very similar to those recorded in 

 table i except that the flowers of sulphur exhibited no toxic ac- 

 tion even to Sclerotinia cinerea and the hydrophobic colloidal sul- 

 phur was only slightly toxic with Botrytis cinerea and Colleto- 

 trichum Gossypii. The hydrophilic colloidal sulphur exhibited 

 the usual degree of toxicity, regardless of the fact that it was 

 a considerable distance from the spore. Toxicity was greatest 

 in all cases at P H 4.0-5.5, as in the previous tests. 



Having determined that the toxic substance is volatile, it was 

 thought necessary at this point to eliminate, if possible, hydrogen 

 sulphide, sulphur dioxide, and sulphur trioxide, as factors. For 

 these tests Sclerotinia cinerea was selected because it has proved 

 to be quite sensitive to the toxic action of sulphur. Spores were 

 placed over a saturated solution of hydrogen sulphide in a Van 

 Tieghem cell and the cultures were incubated at 22° C. for 24 

 hours. Germination was not inhibited. The experiment was re- 

 peated with C olletotrichum Gossypii and Botrytis cinerea with 

 similar results. 



No toxicity could be noted with sulphur dioxide in a concentra- 

 tion sufficient to kill when converted into hydrophilic colloidal 

 sulphur by the addition of hydrogen sulphide. 



Sulphuric acid inhibited growth only because of its acidity, ac- 

 cordingly, in proportion to acidity. Positive tests for sulphur 

 dioxide and trioxide could not be obtained in aerated sulphur 

 suspensions that were toxic to Sclerotinia cinerea. These com- 

 pounds, therefore, do not contribute to the toxic properties of 

 sulphur. 



EXPERIMENT 6. THE INFLUENCE OF 2 ON THE TOXICITY 



OF SULPHUR 



I 



In all of the foregoing tests the only oxygen available was 

 that present in the air enclosed in the closed-ring cells. An ex- 

 periment was conducted to determine the effect of oxygen on in- 

 creasing the toxicity of flowers and precipitated sulphur. Finely 

 ground flowers of sulphur and hydrophobic colloidal sulphur 

 were placed in the slightly buffered mixtures in the same concen- 

 tration as in Experiments 1 and 2. The Van Tieghem cells were 

 placed in Petri dishes, the bottoms of which were lined with filter- 

 paper in which holes somewhat larger than the glass rings were 

 cut, so that the cells might rest on the bottoms of the Petri 

 dishes. A large drop of the sulphur suspension was placed at 



