TYPICAL LESSON PLANS 149 



more usual supply of soil nitrogen that enters through the 

 root hairs in solution in the soil water. From your study 

 of soils and the elements they contain that are used by 

 the plants in making foods, you know that nitrogen is often 

 lacking in the soil and that to supply it with commercial 

 fertilizers is an expensive thing to do. It is very much 

 cheaper to sow clover and let these bacteria gather the 

 nitrogen from the air and in this way give a fresh supply to 

 the soil. 



Instead of harvesting the second crop of clover many 

 farmers plow it under. Why? Because the roots and 

 stems add nitrogen to the soil for other crops, and because 

 the leaves of the clover decay quickly and enrich the soil 

 by a fresh supply of humus. Have the pupils look for 

 other clovers in the neighborhood and bring in specimens 

 for study. Sweet clover and white clover will be found in 

 abundance and in some places alsike clover and alfalfa. 

 Note the characteristics common to these plants. Ex- 

 amine the roots to determine whether or not all have 

 nodules. Study the stem of the white clover. Note how 

 the plant spreads over an area. Why is it a good lawn 

 plant? Have grown in the school garden for a compara- 

 tive study a few specimen plants of other legumes than 

 clovers. Soy beans and cow peas should be grown as 

 they are often used instead of clover as nitrogen-fixing 

 plants. 



BUMBLEBEES.— Eighth Grade 



Problems. — What is the relation of bumblebees to red 

 clover? To what extent do these bees show division of 

 labor? 



