59 



tliermometers as a part of the school-room equipment, interesting 

 experiments can be conducted in determining tlie effect of color and 

 moisture upon the temperature of soils. 



Air in the Soil. 



While that part of the plant wiiich we can see is entirely sur- 

 rounded by air, yet it is necessary that the soil be in such a condition 

 that it can be penetrated by the air. Indeed, growth cannot begin 

 in a soil from which the air is excluded. 



Experiment No. 11. — ^To prove this, put clay soil in a pot, plant 

 seeds and then wet the surface of the soil and puddle or pack the 



^''^ft^lM 



33. — The clover roots iienctrate the soil deeply. 



clay while wet and watch for the seeds to germinate and grow. At 

 the same time put seeds in another pot filled with loose, mellow, 

 moist soil. 



Frequently after the farmer has sown his grain there comes a 

 heavy, beating rain, and the surface of the soil is so packed that the 

 air is excluded and the seeds cannot germinate. If plants are grown 

 in pots and the water is supplied at the top of the soil it may 

 become so hard and compact as to exclude the air and the plants 

 will make a sickly growth. The surface soil must be kept loose 

 that the air can penetrate. 



451 



