DISEASES OF CULTIVATED PLANTS 357 
particles of these compounds which are evidently the effective avents 
in fungicidal action. ‘These insoluble light blue copper compounds 
which, in this divided condition, are held in suspension in the liquid 
give it the characteristic color. The essential needs in making 
Bordeaux mixture are the presence of enough or even an excess of 
the base, calcium (lime), so that none of the copper will remain in 
soluble form as sulfate. This on the other hand involves the more 
or less complete change of the soluble copper into relatively insol- 
uble, blue-colored copper compounds of another sort. 
The philosophy of spray action is based first of all upon the 
absence of injurious effects from the lime products and from the 
copper compounds produced, when sprayed upon green foliage. In 
the second place, upon the effectiveness of these insoluble copper 
compounds through solution in the presence of moisture and carbon 
dioxid in the atmosphere, to destroy or prevent the growth and 
development of parasitic fungi. The time during which these insol- 
uble copper compounds will be effective must depend upon the rate 
of growth in the plant parts and the adhesiveness of the application. 
The essential feature to be remembered is this; the insoluble or 
slowly soluble copper compounds become available by 
solution as needed. Where excess of fungicide is employed this has 
a certain danger upon apple or other foliage during showery 
weather and in all cases the strength is adapted to the host crop. 
Coincident with the spraying period there is frequent complaint 
of injury to apple foliage. Here we have solution effected more 
rapidly than is safe for the host; normally this risk is slight, but 
may be overcome by necessary modifications. Another matter is 
the amount, the number of gallons of the given fungicide to use; 
with more complete spraying appliances and high pressure of appli- 
cation, larger amounts and more complete covering of the parts are 
the rule. Recent results show that when the amount of copper 
in the mixture is near to the danger line these heavier applications 
increase the risk. 
In the early translations from the French the strength of Bor- 
deaux mixture was placed higher than is now the practice. For 
Ohio the following formula has been the rule for many years: 
STANDARD BORDEAUX MIXTURE 
Copper sulfate (blue vitriol).........cccc66 ceeeeeeees 4 pounds. 
Caustic lime (unslaked)..........ccssseseeseeee coneeees 4 pounds. 
Water to make..........ccceee ceeeee cneeeeeeeeneeeseueees 50 gallons. 
This is a 4-4-50 formula—a 2-2-50 formula is also 
used at times. 
In making Bordeaux mixture, the copper sulfate may be dis- 
solved in hot water (about 2 gallons) or better by suspending the 
sulfate contained in cheese-cloth sack, in a large vessel of cold water. 
