TOXICITY OF HEAVY METALS 79 



identical effects with the three different concentrations of Pb(NO 3 ) 2 here 

 used. Concentrations of o.oim, o.O2m and o.o6m Ca(NO 3 ) 2 combined, 

 respectively, with concentrations of o.oooi6m, o.ooo33m and o.ooo66m 

 Pb(NO 3 ) 2 produce practically the same effect on spore germination as does 

 the 0.00005111 concentration of the lead salt alone. It thus appears that 

 for all three very different concentrations of Pb(NO 3 ) 2 , the addition of 

 Ca(NO 3 ) 2 in the proportion of six molecules of the calcium salt to one 

 molecule of Pb(NO 3 ) 2 reduces the toxicity of the latter salt to a point 

 where it almost, but not quite, inhibits normal germination and nearly 

 restricts germinal activity to the formation of appressoria and other swell- 

 ings. To obtain this same condition of germination a simple solution of 

 Pb(NO 3 ) 2 must have a concentration of 0.00005111. 



A similar series of equivalent effects upon spore germination, with the 

 three different concentrations of the lead salt, is shown by taking as the 

 index of physiological activity the prevalence of normal germ tubes in 

 the cultures, as contrasted with swellings and appressoria. This condi- 

 tion of affairs is attained in combination solutions containing, respectively, 

 o.02m Ca(NO 3 ) 2 combined with o.ooo66m Pb(NO 3 ) 2 , o.oim Ca(NO 3 ) 2 

 combined with 0.00033111 Pb(NO 3 ) 2 , and 0.005111 (Ca(NO 3 ) 2 combined 

 with o.oooi6m Pb(NO 3 ) 2 . These three combinations of the two salts all 

 produce practically the same effect on germination as does the concentration 

 of 0.00004111 Pb(NO 3 ) 2 alone. Here the addition of about 30 molecules 

 of Ca(NO 3 ) 2 to i of Pb(NO 3 ) 2 (30:1) reduces the toxicity of the lead 

 salt until it is physiologically equivalent to that of the 0.00004111 solution 

 of this salt alone. 



Combination of Pb(NO 3 ) 2 with Mg(NO 3 ) 2 shows a similar influence 

 of the alkaline earth upon the toxicity of the heavy metal, though with 

 somewhat different concentrations. Equivalent physiological effects were 

 produced by o.ooo66m Pb(NO 3 ) 2 in combination with o.O2tn Mg(NO 3 ) 2 , 

 by 0.00033111 Pb(NO 3 ) 2 in combination with o.oim Mg(NO 3 ) 2 and by 

 o.oooo5m Pb(NO 3 ) 2 alone. Here the addition of about 30 molecules of 

 Mg(NO 3 ) 2 for each molecule of Pb(NO 3 ) 2 in the solution, reduced the 

 toxicity of the latter salt so that it became equivalent, in both combinations, 

 to a simple solution containing 0.00005111 Pb(NO 3 ) 2 . Under these condi- 

 tions most of the germinal activity took the form of the production of 

 appressoria and other swellings, but a small amount of normal germina- 

 tion was observed in all cases. Thus, Mg(NO 3 ) 2 appears to be only about 

 one fifth as effective in reducing the toxicity of the lead salt as is Ca(NO 3 ) 2 . 



Magnesium nitrate was not employed in concentration sufficiently high 

 to inhibit all toxic effects of the lead salt. The nearest approach to normal 

 germination was obtained in a combination solution containing o.O5m 

 Mg(NO 3 )o and 0.00033111 Pb(NO 3 ) 2 , in which about half of the germina- 



