202 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



hanging-drop method, he determined, in a nutrient medium, 

 approximately the relative and absolute toxic properties of 

 many deleterious agents as shown by their influence on spore 

 germination, mycelial development, and fructification. The 

 medium used throughout this study was an infusion of sugar 

 beet, as experiments have shown this to be the most suitable and 

 satisfactory medium for all the forms. The toxicity of the 

 various acids and alkalis towards moulds is shown in detail, and 

 interest centers upon (1) the average inhibiting concentration for 

 germination and development, and (2) the average killing con- 

 centration, the organisms employed being Aspergillus flams, 

 Sterigmatocystis nigra, Oedocephalum albidum, Penicillium glau- 

 cum, and Botrytis vulgaris. 



It was a general rule with all acids and alkalis that when the 

 concentrations were not sufficient to cause distinct injury, 

 stimulation of growth followed the slight retardation, such 

 cultures taking on new vigor and surpassing the controls. Spores 

 of Botrytis were most easily killed, while those of Penicillium 

 offered the greatest resistance. Comparing the results with 

 conductivity data, Clark concludes that the OH ion is more toxic 

 towards fungi than the H ion. It is to be remembered, however, 

 that the hydrogen ion concentration of none of his solutions was 

 known. Nevertheless, this is of special interest when taken in 

 conjunction with data which I shall present later. 



Using distilled water as a medium, Stevens ('98) studied the 

 effect of salts, bases, and acids upon the germination of the 



following 



Macrospor 



Penicillium crustaceum, Gloeosporium musarum, and Uromyces 

 caryophyllinus. As might be expected, germination of most of 

 these species is not perfect in distilled water or else there is con- 

 siderable variability in the results. Abnormal and distorted 

 mycelium appear more frequently in the acid solution than inordi- 

 nary nutrient media. With Macrosporium and Penicillium 

 neither HC1 nor H 2 S0 4 prevented growth, and the behavior of 

 Uromyces towards these acids was quite variable. Further work 

 with alkalis tends to indicate that KOH, NaOH, and NH 4 OH 

 have a low toxic value. Penicillium generally offered the great- 

 est resistance to the different agents. From the data obtained. 





