210 



COMMON DISEASES OF CROPS 



initely, and to endure the temperature of boiling water 

 for perhaps twenty minutes. The parts so protected are 



called spores. The few kinds 

 of bacteria that produce diseases 

 in man do not, however, form 

 spores, and are therefore more 

 easily killed by heat. 



156. Control. The parts of 

 farm plants afflicted with a 

 bacterial disease should be cut 

 out, or pruned away, and then 

 burned, because they cannot be 

 cured. It is often necessary to 

 destroy an entire plant. Care 

 must be taken to prevent diseased tissue from touching 

 healthy parts, because diseases of this nature are conta- 



BACTERIA. 

 Note those which are dividing. 



PLUM ROT. 



Showing four stages from right to left, 

 fungus. 



It is caused by a parasitic 



gious. Crop rotation is often an effective means of keep- 

 ing down a bacterial disease, since the germs in the soil 



