38 SOILS AND PLANT LIFE 



more. Remember that this pie should not have been 

 allowed at any time to lose its moisture. Bring it again 

 into the schoolroom, thaw it out gradually, and put it 

 on the shelf with the others. 



Conclusions. — Break and crumble each of the pies in 

 your hand. Remember that one of them has not been 

 frozen at all, another has been frozen once, the third, twice, 

 and the fourth, three times. Record in your notebook 

 which one crumbled most easily, which one next, etc. 

 What did the freezing do to the particles of soil which 

 had been stuck together by pressure of the fingers while 

 wet? Have you not noticed how much more mellow a 

 soil is in the spring than in the fall? What are some of 

 the advantages of fall plowing? 



EXERCISE 16 



Object. — To determine the effect upon structure of 

 working organic matter into the soil. 



Procedure. — Make a mud pie out of clay as you did 

 in the preceding exercise, only just moisten it instead of 

 making it wet. Make a second one in the same way, but 

 make it of one part sawdust, peat or powdered leaf mold, 

 and two parts clay. Mix the ingredients dry before 

 adding water. Make a third and fourth pie as you did 

 the first two, but using sand instead of clay, then a fifth 

 and sixth one, using silt in the same way. Put the pies 

 in an oven, on the radiator or on the back of the stove to 

 dry them out thoroughly. 



Conclusions. — Crumble each pie carefully in your 

 hands. Which crumbles more readily, the clay alone, or 

 the clay and organic matter? Did the addition of the 

 organic matter have as much effect upon the silt as upon 

 the clay? Did it not have least effect upon the sand? 

 In which soil are the particles smallest? Wovild you say 



