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TEXTBOOK OF BOTANY 



leaves and stems of various plants; "witches' brooms" on hackberry; and 

 peach leaf curl are among the commoner examples. 



5. Leaf spots are dead spots caused by the local growth of parasites in 

 the leaf tissues of the host. The)' occur frequently on leaves of cherry, 

 tomato, rose, and many other plants. 



6. Wilts include various diseases that are first noticeable by the sudden 

 wilting of leaves or of the whole plant. Bacterial wilts of cucumber and 

 cantaloupe are rather common. Damping-off of seedlings and cuttings is 

 a type of wilt disease caused by local infection and weakening of stems 

 near the surface of the soil. 



Fig. 259. Apple infected by the fungus which causes bitter rot of apples. Photo 

 from Ohio Agricultural Extension Service. 



7. Rots are the result of the decomposition of the cell walls of aflFected 

 tissues, such as the soft rot of sweet potatoes, bitter rot of apples (Fig. 

 259), and brown rot of stone fruits. 



8. Blight is the term applied to the sudden dying of leaves, shoots, 

 and blossoms. The fire blight of apple and pear is common wherever 

 these trees grow in America. 



9. Cankers are sunken dead areas on stems in which the bark is 



