CHAPTER XV 



COMMON DISEASES OF OEOPS 



Diseases desperate grown 



By desperate appliance are removed, 



Or not at all. 



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153. What Is a Plant Disease ? Plants have to contend 

 not only with excessive heat and cold and wet and drought, 

 but also, like every living creature, with living enemies. 

 When, however, a young squash plant is killed by a cut- 

 worm, or when a potato plant is injured by potato bugs, 

 we do not usually speak of the plant as afflicted by disease. 

 But we do so speak when the plant's enemy is some minute 

 form of life that exists within it or only in connection with 

 it. A plant disease is any weak or backward condition due to 

 parasitic plants like bacteria and fungi. 



154. Bacteria. Just as a man is likely to be afflicted 

 with tiny plants called bacteria, which cause such diseases 

 as typhoid fever and tuberculosis, so field and garden crops 

 are liable to suffer from certain other kinds of bacteria. 

 Cabbage leaves occasionally show " burnt edges," the work 

 of these germs. Turnips, cauliflower, kale, and other mem- 

 bers of the cabbage tribe may be affected in a like way. 

 The leaves of sweet corn now and then wilt and dry up 

 because their water supply is cut off by the work of 

 bacteria in diseased tissue. On the leaves or twigs of the 

 common pear a " fire blight " often breaks out. The wilt- 

 ing of cucumbers and the soft rot of carrots and other 



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