Toxicity of Copper to Plant Roots 171 



water solution. This fact indicates that the toxicity of copper 

 salts in the presence of soil-water solutions is probably miniinized. 

 In all cases it was observed that root growth was much more 

 vigorous in salty than in distilled water, where no copper was 

 used. Lessened toxicity of copper in salty solutions may there- 

 fore in part be due to greater vigor and resistant qualities of 

 plant cells grown in such solutions. 



2. Copper appears to be equally toxic as sulphate or as basic 

 carbonate. 



3. Corn is probably more sensitive to copper salts than is 

 squash or beans. 



Stimulation Effects in Water Cultures 



In view of the debated question as to stimulation of plant 



growth by minute amounts of copper salts, it is of interest to 



observe that, quite consistently, the most vigorous root growth 



is associated with concentrations of from 0.01 to 0.1 parts per 



million of copper, as shown by details from cultures described 



on previous pages. 



TABLE XIV (a) 



Stimulation Effects of Copper upon Eoots of Plants in Water 



Cultures 



Corn roots grown in well water with Cu(OH)2.CuC03 



Condition 

 Tops of plants showing 

 increased growth at .08 

 and .1 p.p.m. 



Showing stimulation at .01 p.p.m. 



TABLE XIV (h) 

 Bean roots grown in well water with Cu(OH)2.CuC03 



Condition 

 Tops of plants in .08 

 and .1 cultures higher 

 than in .05, .03, .01, and 

 check. 



Showing stimulation at .03 p.p.m. 



