247 



BOTANICAL GAZETTE 



[APRIL 



found to become equitoxic with increasing concentration of the enzyme. 

 Here the relative toxicity of zinc as compared with that of copper 

 decreases with increasing concentration of the enzyme. In both cases 

 the tendency of zinc to lose in relative toxicity with increasing concen- 

 tration of the enzyme is apparent. 



TABLE XVIII: 



Mercury and silver in contemporaneous test 



MERCURY 



SILVER 



8192. 

 4096. 

 2048. 

 1024. 

 512. 



0.05 

 0.04 

 0.03 

 0.00 

 0.00 



Enzyme o. 10 per cent. Incubation 5 hours at 40° C. 



Here the point of total inhibition for copper is the same as with the 

 lower concentration of the enzyme in the preceding table, but the zinc 



TABLE XIX 



MERCURY 



SILVER 



8192. 

 4096. 

 2048. 

 1024. 

 512. 



o. 10 

 o. 10 

 0.07 



0.05 

 0.05 



Enzyme 0.15 per cent. Incubation 5 hours at 40° C. 



fails to inhibit totally and shows plainly that it loses toxicity faster 

 than copper as the concentration of the enzyme increases. 



In Tables XIII and XIV mercury is four times more toxic than 



