32 ELEVENTH REPORT. 



more dilute solution compensated for the more material in the stronger 

 solution. 



A chemical examination of the Bordeaux mixture used for the a])ove. 

 experiments revealed the fact that the copper sulphate must have contained 

 iron, because this was present in the supernatant liquid, and accounts for its 

 toxicity over that ])roducecl by the lime. This is the only explanation for 

 the excessive toxicity of fresh supernatant Bordeaux which is made from 

 commercial copper sulphate and which ]n-actically always contains iron. 

 In the more dilute grades of Bordeaux, which has l^een allowed to stand for 

 a considerable length of time, copi^er appears in the supernatant liciuid in 

 solution as the result of slow decomposition. 



The more imjiortant commercial results to be deduced from these ex- 

 periments are tlu\t I^jordeaux mixture becomes more toxic as it becomes 

 older and consequently may do damage that it would not do if used fresh. 

 Bordeaux reacts readily upon living parts of plants, the precipitate entering 

 into the reaction as shown by the lupine radicles. The amount of such 

 reaction will depend upon the character of the plant substance with which 

 the precipitate comes into contact. 



East Lansing, April 1, 1909. 



