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own spores, and we find a smut-ball where we should have had 
a healthy grain. 
Since the corn-plant is infected mainly through the soil one 
of the best methods of controlling this disease is to prevent the 
infection of the young plants which is best accomplished by the 
rotation of corn with other crops. If corn is grown year after 
year on the same soil the disease becomes worse and worse until 
a very large part of the crop is destroyed. 
¢ 
Fic. 35. Witches’ broom of black spruce, a disease caused by a fungous 
parasite. 
Smut oF Oats. 
Another crop of considerable importance in this country is the 
oat-crop. If we should walk through a field of oats about harvest 
time and look closely at the grain we would find occasionally a 
head in which all of the healthy seeds are replaced by a black 
mass of spores similar to those found in the corn-smut. At 
first sight it might appear that the loss from this disease is too 
