PLANT DISEASES. 



255 



deaux mixture makes the plants distasteful to the cu- 

 cumber beetle and other carriers of the disease, and 

 for this reason has a good effect in controlling its 

 spread. Affected portions of vines should be promptly 

 removed and destroyed. 



EXERCISE. If possible find some garden vegetables that do not 

 look healthy and try to identify the disease they are troubled with. 

 What would you do to prevent these diseases? 



SECTION XXXIX. FIELD CROP DISEASES. 



Grain Smuts. According to 

 the mode of infection, smut 

 diseases of grain crops fall into 

 three classes, of which loose 

 smut of oats, loose smut of 

 wheat and corn smut are com- 

 mon examples. 



Loose Smut of Oats is con- 

 spicuous because the grains are 

 converted into masses of dark, 

 dust-like spores of the fungus. 

 These are shed as the grain 

 ripens, or during harvesting 

 and thrashing; so that seed 

 oats become well dusted with 

 them. When seed with smut 

 spores adhering are planted, 

 the spores germinate as the 

 seeds sprout and the fungus 

 enters the tissues of the tiny 

 seedling oat plant before it ap- 

 pears above ground. Infection 

 does not take place at any later 

 time; but the fungus already in 

 the plant grows upward with it, 

 always hidden, until the plant 

 heads out, and conditions are 

 suitable for spore formation. 



SMUT OF GRAIN. 



