8 MASS. EXPERIMENT STATION BULLETIN 248 



Table 2. Comparative Loss of Vaporized Sulfur and Dusting Sulfur after 



Exposure to Rain. 



the deposit. Dense deposits show very little unoccupied space. Thin deposits 

 show an extremely fine division of sulfur. In both cases distribution is 

 extremely uniform (Plate I, C, D). The uniform distribution of vaporized 

 sulfur on the plants and ground in the greenhouse is impressive. Such an 

 intimate association between the fungus and sulfur is not obtainable with 

 spraying or dusting materials (Plate I, A, B). 



In a series of experiments, Cladosporium spores were exposed in different 

 ways to sulfur vapors (Table 3) and then incubated for 48 hours in Petri 

 dishes. The sulfur was evaporated slowly over an electric hot plate at 

 moderate temperatures with free access to air. The spores were examined 

 for germination at the termination of 48 hours and a final examination was 

 made at the end of 72 hours. Duplicate slides were exposed, one group serv- 

 ing to determine the degree of acid present after exposure to sulfur vapors 

 and the other after incubation. Constant chamber temperatures were main- 

 tained during the exposure of the spores to vaporized sulfur and during the 

 period of incubation in Petri dishes. For these tests individual temperatures 

 between 65° and 90° F. were used. Six tests of each method of technique 

 were made. 



Table 3. Effect of Vaporized Sulfur on Spore Germination. 



Method of Technique 



I. Dry Spores applied to vaporized sulfur re&idue 



II. Dry Spores exposed to vaporized sulfur 



IV. Spores in water drop applied to vaporized sulfur residue 



V. Spores in water drop exposed to vaporized sulfur 



VI. Spores sprayed with water, then exposed to vaporized sulfur. 



VII. Spores sprayed with water after exposure to vaporized sulfur. 



Check. Spores applied dry to clean glass slides 



Check. Spores applied in water drop to clean glass slides 



Average 



Percent 



Germination 



26.1 

 26.6 

 15.9 

 26 6 

 15.1 

 1.6 

 79.1 

 55 8 



This study failed to show that the toxicity of vaporized sulfur is due to 

 its fumes. Varying degrees of control of germination were obtained by all 

 methods of exposure, but instances of total inhibition were obtained only 

 when spores were exposed in water to the vapors (V), or conveyed in water 

 to the residue (IV), or atomized with water (VII) after exposure. It was 

 anticipated that immersion in the sulfur droplets (II) would provide a 

 greater lethal action than when the spores were applied to the dry residue 



