212 



COMMON DISEASES OF CROPS 



of isolating or killing cattle affected by the foot-and-mouth 

 disease. Human beings, of course, are taken care of, and 

 cured if possible, but under such conditions as not to be 

 a menace to healthy people. Valuable cattle are killed, 

 if needful, to check the spread of their disease. And as 



healthy people are vac- 

 cinated as a preven- 

 tion against contagious 

 diseases like smallpox, 

 so healthy plants are 

 sprayed with certain 

 chemicals to ward off 

 disease germs. 



157. Fungi are plants 

 of very low organiza- 

 tion, for they produce 

 neither roots, leaves, 

 nor flowers. The most 

 familiar examples per- 

 haps are toadstools. 

 SHOT-HOLE FUNGUS ON APPLE LEAVES. Like bacteria, fungi can- 

 This fungus is spread by tiny thread- llo t manufacture their 

 like germs, exuding from little swellings , , ,. . , 



on the leaf. own food directly from 



the soil, but must depend 



on other organisms, either living or dead, to support them. 

 Before studying about certain fungi that cause diseases 

 in crops, a few words may be said for them, and for their 

 close allies, bacteria, in that part of their work which 

 befriends the farmer. 



The farmer is greatly indebted to these fungi. With- 

 out their aid, the surface of the earth would be choked 

 up with old undecayed organisms, and much of the 

 food that has once been taken from the soil by living 

 beings would not be returned to it again. Like bacteria, 



