[Vol. 9 



418 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



compounds that were formed in the changed lime sulphur, such 

 as the sulphites and sulphates and the precipitated sulphur. The 

 toxicity of these compounds was determined in the same way as 

 in the preceding experiments. 



The calcium thiosulphate solution did not inhibit germination 

 of any of the organisms used. Similar results were obtained by 

 Armstrong ('21) in his studies on sulphur nutrition of the fungi. 

 Accord ingly, calcium thiosulphate cannot be a factor, even at 

 this high concentration, in the fungicidal value of lime sulphur. 



One cc. of the precipitated sulphur suspension was placed in 

 each of the tubes containing the slightly buffered solution. This 

 made a further dilution of 1:5, making this final suspension 

 equal to that of the original changed lime sulphur, that is, 1:6. 

 The toxicity was determined in the same way as in the preceding 

 tests. The results are given in table i. 



The results were very similar to those obtained with colloidal 

 sulphur. The hydrogen-ion concentration influenced the tox- 

 icity in the same general way. To make sure that this toxicity 

 was not due to the sulphites and sulphates the sulphur was coag- 

 ulated out as in the case of colloidal sulphur and the toxicity 

 again determined. The results were the same. A further test 

 was made, using a 0.1 per cent solution of calcium sulphite, but 

 no toxicity resulted. An attempt was next made to try to further 

 purify the sulphur suspension by fractional centrifugation, in 

 which the centrifuge was run very slowly, thus throwing out the 



d not the insoluble calcium sulphites. By 



the centrifuging 5 or 6 times 



obtained 



which when dried was completely soluble in carbon bisulphide. 

 The results with reference to toxicity were the same as those 

 cited above. 



It must be concluded from these results that the lasting fun- 

 gicidal value of lime sulphur is due almost entirely to the pre- 

 cipitated sulphur, directly or indirectly, and not to the calcium 

 thiosulphate and the insoluble sulphites. The precipitated sul- 

 phur formed in the changed lime sulphur is not in as finely 

 divided state as the soluble colloidal sulphur preparer by the 

 above methods, as was shown by the slow speed with which it 

 could be thrown out of suspension. However, its toxicity was 

 slightly greater than that of the hydrophobic colloidal sulphur 

 in the same concentration. 



