TOXICITY OF HEAVY METALS 85 



growth, and (3) change in phenomena of reproduction. The response to a 

 high concentration was usually death, while addition of a toxic salt in con- 

 centration somewhat below the fatal one stimulated the production of the 

 palmella form, with spherical cells and division occurring in all directions. 

 It is interesting that, with relatively similar concentrations of the salts, 

 (that is at concentrations somewhat lower than those required to 

 inhibit germination) the spores dealt with in the present paper exhibited 

 responses similar to those which Livingston found with his alga ; the pro- 

 duction of appressoria and swellings in this fungus appears physiologically 

 similar to the production of the palmella form in Stigeoclonium. The third 

 type of response discussed by Livingston, change in phenomena of repro- 

 duction, of course finds no parallel m this investigation. 



For convenience of comparison, the limits of the various responses of 

 the fungus spores here dealt with, to the different treatments employed, 

 are presented in table IV. The only nitrate occurring in the table that has 

 not already received attention is the acid. In a series of cultures with 

 HNO 3 the germination at a 0.005111 concentration was practically all normal, 

 while at o.oim and all higher concentrations, no germination took place in 

 the eighteen hour period. The acid prevented germination for the period 

 of eighteen hours, in a o.O2m concentration and killed the spores in 0.5111. 

 No concentration was found, therefore, at which the germination took the 

 form of any of the various abnormal growths found at some concentration 

 with all the other substances used, nor was there any apparent coagulation 

 of the protoplasm at concentrations below that which killed the spores. 

 From these considerations it seems, then, that the various abnormal 

 growths and effects on the protoplasm of the spore cannot be due to 

 acid present in the salt solutions, as a result of hydrolysis of the salts, 

 but must be related, either directly or indirectly, to the metals themselves. 



Turning now to table IV, the different substances are there arranged in 

 the order of the concentration which just allowed normal germination in a 

 period of eighteen hours. In the first column are listed the substances 

 dealt with. The remaining columns are each double. The second column 

 presents the concentrations in which the spores are killed in eighteen hours 

 and fail to germinate later, after transfer to distilled water. Here, as in 

 many other instances, the critical concentrations must not be regarded as 

 definite in the sense of the more exact physical sciences ; the concentrations 

 employed in the experimental series were frequently rather widely separated, 

 and. were this not the case, the variability of the organism in its resistance 

 to toxic substances would render quite useless any attempt to define such 

 critical points with very great accuracy. In all such work as the present, 

 dealing with organisms, the internal conditions of the cells must be as 

 important in determining reactions as are the external ones, and we are 



