SOIL AND SOIL PREPARATION 43 



If it is desired to illustrate this more graphically, the follow- 

 ing device may be employed. 



Place a cube of loaf sugar in a beaker. Pile as much 

 granulated sugar on top as it will hold. Beside this place 

 another cube of sugar without any granulated sugar upon 

 it. Now add a small quantity of red ink to the dish and note 

 rapidity with which it rises through the sugar cubes. 



In which does it rise more rapidly? Can you explain 

 why? Wherein is this exercise like the preceding? The 

 loose aerated stratum on the surface of tilled soil thus pre- 

 vents the too rapid loss of soil water through evaporation. 

 The sugar experiment is not precisely similar to what hap- 

 pens in soil, but the phenomena are analogous. 



Suggestion. To show that germination is hindered or 

 prevented by lack of air in the soil, fill two flowerpots 

 with heavy loam or clay soil and plant some seeds. 



Leave the soil in one flowerpot loose, mellow, and moist; 

 but add enough water to the other to puddle it so that the 

 clay surface becomes packed while wet. 



In which soil do the seeds germinate first ? 



32. EFFECT OF TILLING 



Objects. To study the effect of worms on soils. 



Apparatus. Flowerpots of rich soil, one or two free from worms, 

 one or two containing two or three earthworms, and one or two with 

 five or six earthworms. 



Method. Plant tender seedlings in each flowerpot, water 

 them, and stand them in a place favorable for growth. After 

 several days examine the surface of the soil for worm casts. 

 Continue observations for several weeks, or until definite 

 results are apparent. 



