364 



GROWTH OF PLANTS 



was independent of acidity. Actual contact between the sulfur and spores 

 was not found to be necessary for the production of H2S, since it was found 

 that the reaction can take place through a collodion membrane with the 

 H2S being produced on the spore side and not the sulfur side, as illustrated 



LEAD ACETATE 

 PAPER WHITE 



LEAD ACETATE 

 PAPER BLACKENED 



COLLODION SAC 

 SPORE SUSPENSION 

 SULPHUR PASTE 



Figure 141. The production of hydrogen 

 sulfide by Sderotinia spores separated from 

 sulfur by a collodion membrane. Note 

 that the evolution of hydrogen sulfide 

 takes place on the spore side of the mem- 

 brane and not on the sulfur side. 



in Fig. 141. It is thus evident that the production of H2S takes place on 

 or within the spore. The reaction can even take place across an air space 

 of several millimeters, as shown m Fig. 142. The presence of the sulfur- 

 reducing — SH group was also demonstrated in the spores of Sderotinia 

 fructicola. 



Figure 142. The action of sulfur (S) 

 across an air space on yeast spores (F), as 

 indicated by the blackening of lead acetate 

 paper {P). 



Hydrogen sulfide gas was found to be highly toxic to the spores of these 

 eight fungi, the toxicity varying with the different species. When these 

 eight species were compared as to their sensitivity to H2S and to sulfur 

 the order was identical. The order of decreasing sensitivity was as follows: 

 Venturia, Uromyces, Puccinia, Sderotinia, Macrosporiitm, Pestalotia, 

 Glomerella, and Botrytis. When the production of H2S by these spores was 

 expressed in units equal to the amount of HoS required to reduce their ger- 

 mination 50 per cent, the following relation appeared, as may be seen in 

 Table 38: the four sulfur-sensitive species {Venturia, Uromyces, Puccinia, 



