104 EXPERIMENTS WITH PLANTS 



well in water to form a paste. Place it in a fruit -jar, 

 fill the jar with water, fasten the cover on, shake the 

 jar well for some time, and then allow it to stand until 

 the soil settles to the bottom. Examine the soil after 

 it has settled. The coarse material on the bottom is 

 sand, above this is finer material consisting mostly of 

 clay, the finest particles of which remain in suspension 

 in the water, making it turbid. On the top of the 

 water floats a little vegetable matter which in its de- 

 composed state is called humus. These three constitu- 

 ents of the soil have very different properties, which 

 should be clearly understood, since the entire fertility 

 of the land depends on a proper admixture of these 

 constituents. A more complete separation may be 

 effected by first skimming off the vegetable matter, then 

 shaking up the soil again in water and pouring the 

 turbid water through a cloth. Continue the process 

 until the clay is all removed : the sand will remain in 

 the bottom of the jar. A still better separation may be 

 effected by siphoning water from a pail through a 

 piece of rubber tubing into a tumbler (with vertical 

 sides) which contains earth (this should be constantly 

 stirred with a pencil during the passage of the current) ; 

 the current may be regulated by compressing the 

 rubber tubing; the overflow from the tumbler should 

 be caught in a second tumbler, of larger size, placed 

 beneath the first. Beginning with a weak current, the 

 finest particles will be carried over into the second 



