TOXICITY OF VARIOUS NITRATES TO MONILIA SITOPHILA 631 
in starch media. A comparison of equimolecular concentrations 
shows that of all the nitrates used, potassium nitrate is the least 
toxic and zinc nitrate is the most toxic to Monilia when it is grown 
in a starch medium. Beginning with the least toxic, the order of 
toxicity of the nitrates in starch media is as follows: potassium 
nitrate, calcium nitrate, sodium nitrate, barium nitrate, urea 
nitrate, ammonium nitrate, aluminum nitrate, ferric nitrate, 
silver nitrate, and zinc nitrate. Having thus determined the 
degree of concentration at which the different nitrates are toxic 
to Monilia sitophila in starch media, experiments were made in 
which the organic part of the medium was varied for the purpose 
of determining whether or not the toxicity of these salts can be 
modified by the presence of one or another of the organic sub- 
stances commonly used in making media. The organic substances 
tried are peptone, glucose, fructose, and galactose. The results 
obtained in these experiments are shown in TABLES III to VIII. 
As shown by TABLE III, barium nitrate in peptone media at a 
concentration of 0.133 molar inhibits the germination of the 
spores of Monilia. In a starch medium containing barium 
nitrate at a concentration of 0.156 molar, the spores germinate and 
produce a small amount of mycelium. This shows that barium 
nitrate is more toxic in peptone media than in starch media. 
No concentration of barium nitrate shown in TABLE III was of 
sufficient strength to inhibit germination and growth in the 
presence of glucose. There was, however, a very small amount 
of mycelium in the media containing the barium nitrate at a 
concentration of 0.167 molar. This indicates that the toxic dose 
in glucose media is near the concentration 0.167 molar. The 
toxicity of barium nitrate in starch media and in glucose media is 
approximately the same. Its toxicity in peptone media is much 
greater than in glucose media or in starch media. In fructose 
media its toxicity is approximately the same as in starch and. 
glucose media but is much less than in peptone media. At a 
concentration of 0.1 molar, barium nitrate in the presence of 
galactose inhibits the germination of spores. Its toxicity in 
galactose is approximately the same as in peptone, but is much 
greater than in starch, glucose, or fructose. 
At a concentration of 0.033 molar, aluminum nitrate in peptone 
