THE FARM, AND OUR FOOD SUPPLIES 155 



Wet some clay in an evaporating dish, and then note its 

 feeling and odor when rubbed between the fingers. Note 

 the odor and feeling of shale and of slate when wet. 



SOIL CONDITIONS FOR PLANT GROWTH 



1. Recall (a) the definition of solution; (6) why sub- 

 stances remain undissolved. Test the solubility of bits of 

 crayon and of limestone (a) in water; (b) in hydrochloric 

 acid. Explain any differences in their behavior. 



Whence comes the water in the sap of plants ? How is it 

 possible for food materials in the soil to get into the plant 

 for its use in growth and fruitage? What change in a sub- 

 stance in the soil must often precede its solution by the soil 

 water ? , 



2. Observe the surface of any piece of stone that has been 

 dipped into water. Explain what is noted. If the stone is 

 now broken into several pieces, and all these are dipped into 

 water, what is true (a) of the extent of their surfaces now ; 

 (b) of the amount of water clinging to these surfaces ? 



Break a blackboard crayon into piece after piece ; fit the 

 several pieces together again, and then separate them anew. 

 What is manifest as to the extent of exposed surfaces of the 

 crayon before and after it is broken into pieces? 



What would seem probable of the amount of exposed sur- 

 face, and of the adhering film of water (film-water), if division 

 of rock materials should be continued to the size (a) of sand ; 

 (b) of dust particles? 



3. Have three test tubes about one third full and well 

 settled by jarring, one with coarse sand, one with loam, and 

 one with silt. Into each pour the same amount of water, 



