[Vol. 9 



404 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



History 



The generally employed sulphur sprays, namely, flowers of 

 sulphur and the various sulphide compounds, have been only 

 partially effective in controlling fungous diseases. It will not 

 be necessary in this paper to go into a historical discussion of the 



effectiveness of these sprays, as such discussions are reported 

 frequently by agricultural experiment stations and horticultural 

 societies in bulletins and spray calendars and my own conception 

 of the practical problems involved will be stated below. This 

 work has to do largely with the fungicidal properties of sulphur. 



The toxicity of the flowers of sulphur has been attributed to 

 several compounds, of which hydrogen sulphide, sulphur dioxide, 

 sulphurous and sulphuric acids, and volatile sulphur are more 

 often given. Pollacci ('07) believes that sulphur is transformed 

 into sulphuretted hydrogen, the vapors of which have a very 

 energetic action on the fungi. This view, however, has received 



but little support and has been proved untenable by Bourcart 

 ('13). He was unable to collect any of this gas on passing air 

 from sulphur through solutions suitable for retaining the gas. 

 Foreman ('10) could obtain no inhibition of germination with 

 spores of Botrytis cinerea, using a saturated solution of sulphu- 

 retted hydrogen. Similar results were obtained by Barker, Gim- 

 ingham, and Wiltshire ('20). It is at present generally accepted 

 that hydrogen sulphide is not a factor as a fungicidal property of 

 sulphur. 



The view that the toxic action of sulphur is due to sulphur 

 dioxide has received considerable support. Sostegni and Mori 

 ('90), Blodgett (13), Butler (17), and Kuhl ('21) conclude that 

 the toxic property of sulphur is due to this gas. They believe 

 that the gas is slowly produced by the oxidation of the sulphur. 

 In the papers cited there is little substantiating experimental 

 evidence, other than the fact that the toxic compound is volatile. 

 Contrary views are held by Bourcart (13) who states that "Sul- 

 phurous acid must not be dreamt of; 1/40,000 of this acid in 

 the air would burn the leaves." In a series of experiments he 

 could not collect any sulphur dioxide evolving from si.lphur at 

 temperatures up to 50° C. Barker, Gimingham, and Wiltshire 

 ('20) obtained good germination of spores of Nectria ditissima 

 in a 1 : 100 solution of sulphur dioxide. Closed-ring exp sriments, 

 however, gave limits of .005 per cent and .0005 per cent for the 

 germination of spores of Sclerotinia fructigena, Fusicladium den- 



