Plant Diseases 
323 
be added to the rest of the water. The lime, which should 
be of the finest quality, should be stirred up into a milky 
liquid. It should then be poured into the liquid containing 
the copper sulphate, which, by the way, should always be 
put into a wooden vessel. The mixture should be thor- 
oughly stirred, and is then ready for use. This will keep 
for a week, but it is better to make it as required. 
Bordeaux mixture should be put on with a sprayer, as it 
is then possible to get at the under surface as well as the 
top of the leaves. As this is a preventive, and not a cure, 
it must be put on when it will act as such, that is, before 
the disease has a chance of getting a hold upon the Po- 
tatoes. About the middle of June is generally considered 
to be a safe time for the first spraying, the disease seldom 
making its appearance before that date. A second spray- 
ing may be given about the middle of July, and a third 
about the middle of August. This, if the spraying has 
been thoroughly done, should keep the crop free from 
disease. 
BLACK SCAB 
This disease is even more terrible than the last. It 
causes large warty growths on the tubers, and sometimes 
even on the stems, when there is a bad attack of it. Very 
little is yet known about its life-history, but when a crop 
of Potatoes is attacked by it, the disease will remain in the 
ground for five or six years. The warts are full of tiny 
little spores or seeds, and when they burst, the spores are 
liberated in countless numbers into the soil. These attack 
the potatoes that in future years may be planted in this 
soil. The terrible thing about these spores is the long 
