CHAPTER XVII 1 

 r 



DISEASES OF PLANTS 



IN our country alone the loss from plant diseases 

 amounts to many millions of dollars each year. Nearly 

 all of this can be avoided. We must first find out what 

 causes the disease. We can then usually find some way 

 to check it. 



This loss is mostly caused by tiny plants called fungi. 

 If you wish to see what they are like, put a bit of moldy 

 bread on a piece of wood in a saucer and cover it with a 

 tumbler. Pour a little water into the saucer to keep 

 the air moist. Soon a white growth is seen. If you 

 look closely at it, you will see that it looks like a mass of 

 threads. You can see that the threads have branches 

 (figure 130). Most fungi are such masses of branching 

 threads. Even a bit of toadstool looks under the 

 microscope like a mass of such threads. 



In place of seeds the fungi have tiny spores, so small 

 that they cannot be seen by the naked eye. Each one 

 of the little black bodies shown in figure 130, which are 



1 The teacher is especially advised to take up only one or two 

 typical forms, which can easily be obtained in his locality, for illus- 

 tration. 



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