LABORATORY EXERCISES 267 



8. What are the most serious insect pests in your county? How 

 may each be controlled? 



9. What are the most useful insects in the region? Do insects x do 

 more harm than good? 



10. Complete the following reaction which takes place in preparing 

 Bordeaux mixture: 



Cu SO 4 + Ca (OH) 2 = ? 



11. What plants are commonly sprayed in your county? What 

 spray is used? When is it applied? What is the cost of the sprayer? 

 The cost of the materials? Of the labor? Does the spraying pay? 



LABORATORY EXERCISES 



62. Bacteria and Molds. 



Materials. Three test tubes, cotton, boiled potato or fruit (apple- 

 sauce is good); three 'apples, one partly decayed. 



Fill each tube about one-third full of apple-sauce or boiled potato. 

 Plug each one with cotton. Set one aside. Put the other two into a 

 pail of water and boil for half an hour. After boiling, set one tube aside 

 with the cotton undisturbed. Take the cotton from the third tube 

 and leave it out for half an hour or more, then put it in again. Leave 

 these for a few days and see what happens. Account for the difference. 

 Is it desirable to leave canned fruit open a few minutes before covering, 

 after cooking? Why? 



Prick one of the sound apples in several places with a pin which 

 has been sterilized by holding it in a flame. Put the pin into the rotten 

 apple and then into the other sound apple Repeat this in several places. 

 Set the two sound apples aside for about a week. What happens? 

 What is one value of the skin to an apple? Why should fruit be picked 

 and handled with care? 



63. Bacteria. 



Materials. Compound microscope magnifying 500 to 1,000 diam- 

 eters, if the school has such a microscope or can secure the use of one 

 temporarily. Examine some stagnant water, or some water in which 

 seeds or bread have been standing for a day or so. This will contain 

 many forms of bacteria and other living things. Most of the bacteria 

 are small, short rods. In many cases there are longer rods made up of 

 two or more plants fastened end to end. Each of the plants is a single 

 cell. They multiply by the simple division of each plant into two, 



