47 



germination, with different concentrations of the lead 

 salt, is shown by taking as the index of physiological act- 

 ivity the prevalence of normal germ tubes in the cultures, 

 as contrasted with swellings and appressoria. This condition 

 of affairs is attained in corahination solutions containing, 

 respectively, C.02ra Ca(N03)2 combined with C.0CC66m 

 PbCNCgjg, C.Olm Ca(N03)2 combined with C.0CC33m PblNOg)^, 

 and C.C05m Ca(NC3)2 combined with C. 000 16m PbCNCjlg- These 

 three combinations of the two salts all produce practically 

 the same effect on germination as does a concentration of 

 C.CC0C4m Pb(NC3)2 alone. Here the addition of about 3C mol- 

 ecules of Ca(NC3)o to 1 (30:1) of ?b(N03)2 ^®^^<^®s the tox- 

 icity of the lead salt until it is physiologically equival- 

 ent to that of a C.O00C4m solution of the lead salt alone. 



Combination of Pb(NC3)2 with Mg(NC3'2 shows a sim- 

 ilar influence of the alkaline earth upon the toxicity of 

 the heavy metal though with somewhat different concentrat- 

 ions. Equivalent physiological effects were produced by 

 C.C0066m Pb(N03)2 in combination with G.02ra Mg(N03)o, by 

 0.0C033m Pb(NC3)2 ^^ combination with O.Glm Mg(N03)2 and by 

 O.OOOCSm Pb(NC3)2 ^lone. Here the addition of about 30 

 molecules of I-!g(N03)2 for each molecule of Pb(N03)2 in the 

 solution reduced the toxicity of the latter salt so that it 

 became equivalent, in both combinations, to 3 simple sol- 

 ution containing 0.00006m PbCNCsJo. Under these conditions 

 most of the germinal activity took the form of the produc- 



