1902] TOXIC PROPERTIES OF COPPER COMPOUNDS 41 
than the Paris green was to be expected, inasmuch as it showed 
on analysis 8.3 per cent. soluble As,O, as compared with 1.8 
per cent. soluble in the sample of Paris green. That the 
ammoniacal solution of CuCO, is a more effective fungicide than 
Bordeaux mixture for the amount of copper used does not follow 
from the showing made in this figure. These tests were made 
in closed cells where the excess of ammonia was indefinitely 
retained, whereas under orchard conditions this evaporates in a 
few hours at most, and exerts practically no fungicidal value. 
It would be beyond the province of the present paper to give 
a detailed account of my experiments on the toxicology of the 
Bordeaux mixture. These are of greater interest to horticultur- 
ists than to botanists. I shall mention briefly, however, the 
more important experiments and state the conclusions arrived at 
from this study. 
Just how the insoluble copper hydroxid of the Bordeaux 
mixture sprayed on leaves has protected them so thoroughly 
from the ravages of parasites has long been a mystery to the 
chemist and physiologist alike. Various hypotheses have been 
propounded from time to time, but up to the present no satis- 
factory explanation has been given. A very careful review 
of the current hypothesis may be found in Swingle’s paper.” 
His own suggestion that it might be possible that the fungi 
themselves, by secretions or excretions, might be able to aid in 
the solution of the copper has proved a happy one. As already 
mentioned, most animal and vegetable decoctions have a greater 
or less power of dissolving insoluble copper compounds. 
This power is particularly noticeable in the fungi. An infu- 
Sion of Agaricus campestris, and infusions and decoctions of 
various parasitic fungi, dissolve copper hydroxid very quickly 
and in sufficient quantity to inhibit the germination of any fun- 
Sus tested. Spores of various fungi placed in a mixture of 
Cu(OH), and water were killed in a short time, while other 
Spores of the same species, placed in similar mixtures of Fe(OH), 
_“SWINGLE, W. T.: Bordeaux mixture. Bull. no. 9. Div. Veg. Phys. and Path. 
U.S. Dept. Agric. 1896, 
