THE DISEASES OF PLANTS 



ID/ 



that does not show a distinct line of separation between diseased and 

 healthy wood? If so, the bacteria are still living in the cambium. 

 Cut out a small bit of the diseased portion and insert it under the 

 bark of a healthy, juicy twig within a few inches of its tip and watch 

 it from day to day. Does the tree " catch " the disease ? This experi- 

 ment may prove to you how easily the disease spreads. If you should 

 see any drops like dew hanging from diseased twigs, touch a little 

 of this moisture to a healthy flower and watch for results. 



Cut and burn all diseased twigs that you can find. Estimate the 

 damage done by this disease. 



Farmers' Bulletin No. 153, on Orchard Enemies, published by the 

 Department of Agriculture, Washington, D.C., can be had by writing 

 for it, and will help your father much in treating fire blight. 



Oat and Wheat Smuts. Let us go out into the oat or 

 wheat field and look for all the blackened heads of grain 

 that we can find. How many are there ? To count accu- 

 rately let us select an area one foot square. We must 

 look sharply, for many 

 of these blackened 

 heads are so low that 

 we shall not see them 

 at first glance. You 

 will be surprised to 



find as many as thirty 



r ' FIG, 91. A THREE DAY OLD 



or forty heads so WHAT PLANT 



blackened in every 

 hundred. These 

 blackened heads are due to a plant disease called smut. 

 When threshing time comes, you will surely notice a 

 great quantity of black dust coming from the grain as it 

 passes through the machine. The air is full of it. This 

 black dust consists of the spores of a tiny fungus plant. 



Smut attacks plants only about this age 



