THE DISEASES OF PLANTS. 



spores in the case of trees and shrubs is bluestone (also known 

 as sulphate of copper). When the fruit grower sprays his trees 

 to check disease on the branches or leaves or fruit he uses a 

 solution of bluestone. Sometimes he makes a mixture of Paris 

 green and bluestone, the Paris green being to kill all insects 

 that eat the leaves, and the bluestone to destroy the spores or 



Fig. 43. Two forms of minute plants growing in leaves and in fruit 

 of plants, causing disease ot" plants. Very much enlarged. 



seeds of disease. There are so many different forms of disease 

 (rusts, smuts, mildews, blights, etc.) that we have not space to 

 mention them. But we shall here give only the simplest modes 

 of preventing disease. Smut, in growing wheat, generally comes 

 from wheat that has grown in fields where smut existed the year 

 before, that is, the wheat when sown had the spores of smut 

 already in the grain. The disease then can be prevented by 

 destroying the spores in the seed that is sown. Make a solution 

 of one pound of bluestone or copper sulphate in twenty-four 

 gallons of water. Soak the grain to be sown in this solution for 

 from twelve to sixteen hours. Then the seed may be dipped in 

 lime water for five minutes. After being thus treated it may be 

 sown and no smut will appear. Sometimes the spores of smut 



