201 
always effective; but, if planted on clean land, even badly 
scabbed seed potatoes will yield a clean crop if soaked in a weak 
solution of corrosive sublimate. 
The discovery that certain diseases can be prevented by sprink- 
ling plants with a solution of copper sulphate mixed with milk of 
lime marked an important epoch in the treatment of plant dis- 
eases. This mixture, known as Bordeaux mixture from the 
town in France near which its use was accidentally discovered, 
is now the standard remedy for a large clase of diseases. In the 
case of many orchard and garden crops, spraying with Bordeaux 
mixture is as much a recognized part of proper culture as is the 
tilling of the soil. As first used the mixture was simply spat- 
tered over the leaves by means of a whisk broom. This method 
was unsatisfactory, as it was slow and did not secure a sufficiently 
even distribution of the liquid. Thanks to American ingenuity 
and particularly to the efforts of the late C. V. Riley then chief 
entomologist and of B. F. Galloway now chief of the Bureau of 
Plant Industry of the United States Department of Agriculture, 
suitable pumps and spraying nozzles were devised, by means of 
which plants can be quickly and evenly covered with this or 
other liquids in the form of a fine mist-like spray. Other com- 
pounds of copper have also been found to have strong fungicidal 
properties, but none are so generally useful as the Bordeaux 
mixture. When properly made and applied it does not injure 
the foliage except of a few particularly delicate plants and as it is 
not easily washed off by rains its effects are more lasting than 
with other fungicides. It is now the standard remedy for potato 
blight, grape rot and mildew, apple scab, peach leaf curl anda 
long list of similar diseases. It should always be remembered 
however that, except in the case of a few external parasites, 
spraying is a preventive measure and not a cure. Sprays cannot 
reach internal parasites when once established, but by coating 
the surface they prevent the germination of spores that find a 
lodgment there and thus prevent infection. The importance of 
early spraying before a disease makes its appearance, and of 
thorough work in reaching all exposed parts of the plant will be 
apparent from these facts. 
