128 SOILS AND PLANT LIFE 



spores of the brown rot of the plum. The apple scab is 

 spread from diseased fruit and leaves. 



Fifth : by insects. Insects, which come to attack the 

 plants, often bring with them from other plants the spores 

 of disease. The first step, then, in the control of such 

 diseases is to destroy the insects. 



98. How to prevent the Spread and Growth of the 

 Spores of Disease. — (1) Spores on the Seed. — The first 

 step in preventing propagation by spores clinging to seeds 

 is seed selection. Since many diseases are spread in this 

 way, a careful farmer tries to select clean seed from clean 

 fields. It is of course impossible to examine each seed of 

 the oats or wheat as might be done with potatoes. In 

 this case, something must be applied which will kill the 

 spores but not the seed. The methods used for the con- 

 trol of oat smut will illustrate this. 



EXERCISE 36 



Object. — To learn how to treat oats for loose 

 smut. 



Procedure. — Put a peck of oats in the bottom of a 

 box. Make a solution of formalin in water by adding 

 5 cc. of 40 per cent formahn to 1600 cc. of water. This 

 is in the proportion of one pint of formalin to forty gallons 

 of water. 



With the hands, sprinkle one quart of this solution 

 over the oats in the box and stir them thoroughly with a 

 fire shovel or stick so that every kernel will become 

 moist. Now cover them with a gunny sack or otherwise 

 so as to prevent the escape of the pungent gas which is 

 given off by the formahn. After four or five hours, remove 

 the cloth and spread the oats out on a floor, table or other 

 surface until thoroughly dried. 



