Dec 1922] 
RUTH — EFFECT OF BORDEAUX MIXTURE 
537 
Millardet and Gayon because of the large amounts of soluble copper they 
used in their experiments and the insolubility of the Bordeaux precipitate. 
Pickering (1910, pp. 113-115) concludes from his experimental work that 
penetration takes place, and that the carbon dioxide of the air is the dis- 
solving agent (1910, pp. 27-36). Bain's very careful investigations (1902) 
have sustained the hypothesis of penetration. Bain (1902, p. 88) states 
his conclusions as follows: 
From all the evidence presented on the preceding pages, there can remain Httle doubt 
that copper is absorbed by the leaves of plants sprayed with Bordeaux mixture. ... Of 
course, the most conclusive and only final evidence of the entrance of the copper into the 
tissues of the leaf is to demonstrate its presence there by an appropriate test. The writer 
has made no experiments in this direction. 
The belief of Millardet and Gayon in the actual penetration of copper 
receives further support from Schander (1904) and Ewert (1905). Schander 
believed, however, that the action of rain and dew is seldom of direct 
importance in dissolving copper salts from Bordeaux mixture because of 
the insolubility of the precipitate, and that in many plants, e.g., in the bean 
and apple, the entrance of copper occurs through the hairs as the result of 
their excretion of an alkaline substance, or through glands in the case of 
other plants, like Fuchsia and Oenothera, following the excretion of acidic 
substances. 
That the physiological effects of Bordeaux mixture are due to the 
penetration of copper, not only in solution but in solution in the ionic state, 
seems very probable if we consider the indirect evidence supplied by the 
work of Kahlenberg and True (1896) and Heald (1896), in connection with 
that of Bain (1902), Clark (1902), and Pickering (1908, 1910). Kahlenberg 
and True, and Heald, working with seedlings in very dilute solutions of 
copper salts, proved that the toxicity of the dissolved copper salt was 
directly proportional to the concentration of copper ions in the solution. 
Bain (1902, pp. 42-52) showed that sprayed peach foliage is not injured 
unless liquid water is present on the leaf. One would expect these results 
in view of the probable effect of the above-named substances in increasing 
or decreasing the concentration of copper ions in the Bordeaux suspension. 
Bain also showed (1902, pp. 36-44) that certain salts, for example, calcium 
chloride, calcium sulphate, and calcium nitrate, produce an increased 
Bordeaux injury, while lime and various carbonates have a tendency to 
prevent it. Clark (1902) and Pickering (1910, pp. 143-145) have shown 
that potassium sulphate decreases the toxicity of copper sulphate, and 
Pickering (1908, p. io6j has shown that sodium chloride increases it. 
Potassium sulphate and sodium chloride would modify the ionization of 
solutions of copper sulphate in a manner corresponding to the decreased 
and increased injury. 
Besides the change in the concentration of copper ions, antagonisms, 
such as that of copper and calcium which has been demonstrated by True 
