ACTION OF FUNGICIDES 



255 



of absorption of sulfur vapor and its reduction to hydrogen sulfide within 

 the spore. Thus, the spores of susceptible species destroy themselves. 

 It is not thought that the hydrogen sulfide evolved from leaves or other 

 spores is absorbed in lethal quantities under natural conditions. 



0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 



Concentration -milligrams per liter 



Fig. 51. Toxicity of hydrogen sulfide to urediospores of Uromyces caryophyllinus 

 and Puccinia antirrhini and to conidia of Venturia inaequalis, Sclerotinia americana, 

 Macrosporiuni sarcinaeforme, Pestalotia stellata, Glonierella cingulata, and Botrytis sp. 

 (Courtesy of McCallan and Wilcoxon, Contribs. Boyce Thompson Inst. 3: 31, 1931.) 



Liquid lime-sulfur is a common spray material and is prepared by 

 boiling sulfur and calcium hydroxide together. The chief active ingre- 

 dient is calcium polysulfide. After deposition on leaves the calcium 

 polysulfide is quickly decomposed, yielding sulfur and calcium sulfide, 



Table 45. Comparison between the Toxicity and the Production of Hydrogen 

 Sulfide, Expressed in Units Equal to the Amounts of Hydrogen Sulfide 

 Required to Reduce Germination 50 Per Cent 

 (McCallan and Wilcoxon, Contribs. Boyce Thompson Inst. 3, 1931.) 



