254 



PHYSIOLOGY OF THE FUNGI 



There is now general agreement that hydrogen sulfide is the common 

 toxic compound produced from sulfur. Not only is hydrogen sulfide 

 toxic to fungus spores, but the mechanism for its production is also pres- 

 ent. It is known that hydrogen sulfide is produced from sulfur both by 

 the treated plant and by the fungus spores, 



McCallan and Wilcoxon (1931) made qualitative tests for the ability 

 of the spores of 17 species of fungi to produce hydrogen sulfide from sulfur. 



All produced this substance, but in 

 varying amounts and at varying 

 rates. They showed that the spores 

 need not be in direct contact with 

 solid sulfur to produce hydrogen 

 sulfide. Figure 50 illustrates the 

 method used by these investigators 

 to demonstrate this phenomenon. 



These authors investigated the 

 toxicity of hydrogen sulfide to the 

 spores of eight species of fungi. 

 These experiments were performed 

 in a flowing stream of air which con- 

 tained known amounts of hydrogen 

 sulfide, and the concentration in the 

 water droplet in which the spores 

 were suspended was calculated from 

 Henry's law. These precautions are 

 necessary because hydrogen sulfide is 

 unstable. Neglect of this fact by 



LEAD ACETATE 

 PAPER WHITE 



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COLLODION SAC 

 SPORE SUSPENSION 

 SULPHUR PASTE 



Fig. 50. The production of hydrogen 

 sulfide by Sclerotinia spores separated 

 from sulfur by a collodion membrane. 

 Note that the production of hydrogen 

 sulfide takes place on the spore side of 

 the membrane and not on the sulfur 

 side. (Courtesy of McCallan and 

 WUcoxon, Contribs. Boyce Thompson 

 Inst. 3: 26, 1931.) 



earlier investigators led to an underestimation of the toxicity of hydrogen 

 sulfide. These results of McCallan and Wilcoxon are presented in Fig. 

 51. From these curves it is seen that spores of Venturia inaequalis, 

 Uromyces caryophyllinus, and Puccinia antirrhini are inhibited by very 

 low concentrations of hydrogen sulfide, while the spores of Botrytis sp. 

 and Glomerella cingulata are scarcely affected by ten times as much 

 hydrogen sulfide. By increasing the hydrogen sulfide concentration to 

 60 p. p.m., complete inhibition of germination of the spores of these two 

 species was obtained. The spores of these eight fungi were shown to 

 produce varying amounts of hydrogen sulfide per unit weight of spores. 

 Whether hydrogen sulfide produced by spores would prove toxic would 

 therefore depend upon the ability of the particular spores to produce 

 hydrogen sulfide and the sensitivity of the spores to this substance. The 

 correlation is shown in Table 45. 



The actions of sulfur and hydrogen sulfide are parallel, and it may be 

 concluded that sulfur is toxic to the spores of certain species by virtue 



