SUGGESTIONS 121 



PRACTICAL QUESTIONS 



1. What is the relation of the soil to plants? 2. How does pul- 

 verizing the soil aid the growth of plants? 3. Name the elements 

 needed by plants. 4. What are the so-called three great agri- 

 cultural elements? 5. Give two characteristics of nitrogen; of 

 phosphorus ; of potassium. 6. How do plants obtain their nitrogen ? 



7. What is the function of nitrogen? Of phosphorus? Of potassium? 



8. Distinguish between plant food and available plant food. 



HOME EXERCISES 



1. Dig up carefully several different farm plants ; then measure 

 and draw their roots. Are there any farm plants which send their 

 roots into the subsoil ? In case of corn, how near to the surface do 

 the roots extend ? Can you see whether roots move to or from the 

 more moist parts of the soil ? 



2. Is it possible to overfeed a plant? Try it in the garden by add- 

 ing a large quantity of fertilizer or compost to a plant. Take notes 

 from week to week on the behavior of the plant. 



3. Ask the fertilizer man for a small quantity of nitrate of soda, 

 acid phosphate, and muriate of potash. He can obtain these plant 

 foods from dealers at a trifling cost. Add a little of each of these 

 substances to different plants on your plot, and note and describe the 

 results. Write to the county agent for details in working out 

 this exercise. 



SUGGESTIONS 



1. It would make the subject very real to have in the schoolroom 

 a small sample of pure phosphorus and potassium ; a half ounce 

 of each would answer. Supplies of this nature are cheap, and can be 

 bought at any of the supply houses listed in the appendix. The 

 burning of a bit of potassium on water is an especially striking 

 experiment. Phosphorus must be handled with great care. 



2. To show that the air contains about four fifths nitrogen, burn 

 up the oxygen contained in the air in an ordinary wide-mouthed 

 bottle. Proceed as follows : Take a splint of wood about six inches 

 long. Light this at one end and insert the lighted end into an inverted 

 bottle which is then immersed in water. Measure the quantity of 

 water that arose in the bottle to take the place of the oxygen consumed. 

 What is left in the bottle is mostly nitrogen. What per cent is it? 



