Lewis Knudson 165 



the fact that both develop in moistened gall nuts, which contain per 

 dry weight 60 per cent of tannic acid, is evidence that for these two 

 organisms the tannic acid is not toxic. 



Toxicity of tannic acid for Aspergillus flavus and Aspergillus oryzae. 

 An experiment was conducted to determine the growth at various 

 concentrations of tannic acid with and without 10 per cent cane 

 sugar. In one case tannic acid (Merck's tested reagent) was 

 added to solution B; in the other, tannic acid + 10 per cent sugar 

 was used. Test-tube cultures with 15 cc. of the solutions were em- 

 ployed. The results in general showed that these two fungi develop 

 normally in the presence of 2.5 per cent tannic acid, but greater 

 concentrations decrease the rate of germination and inhibit the 

 growth. In the 15 per cent concentrations of tannic acid, after 

 nine days, only one-third of the surface was felted. Up to 7.5 

 per cent concentration the entire surface was felted. 



Conclusion and discussion. The experiments on the toxicity 

 of tannic acid indicate that of aU the organisms tested, Asper- 

 gillus niger and Penicillium sp}'^ are best adapted for the tannic 

 acid fermentation. These two organisms were, therefore, selected 

 for more detailed investigation, though the other two organisms 

 previously mentioned were also reserved for further study. 



Since the above experiments were made, a bulletin has appeared 

 on the toxicity of tannin by Cook and Taubenhaus.^^ The major- 

 ity of a large number of parasitic organisms tested by them with 

 respect to the toxicity of tannin show retardation of growth" at 

 from 0.1 per cent to 0.8 per cent of tannin. The few saprophytic 

 forms tested exhibit a more marked resistance. My own experi- 

 ments indicate also that the saprophytic forms can withstand 

 relatively higher concentrations of tannic acid than the parasitic 

 forms. 



2^ See appendix for description of this organism. 



" M. T. Cook and J. J. Taubenhaus : The Relation of Parasitic Fungi to 

 the Contents of the Cells of the Host Plant, Delaware Agric. Exp. Station, 

 Bulletin 91, 77 pp., 1911. 



