THE WORK OF ROOTS 105 



tumbler. When this has been accomplished and the 

 water runs clear, remove the second tumbler, substi- 

 tute another, and increase the strength of the current. 

 By continuing in this way the soil may be separated 

 into numerous portions, in each of which the size of the 

 particles will be confined within certain limits. The 

 time which the particles require for settling in these 

 various portions is of importance. Make notes on this 

 point. 



Sand. — Sand is made up of larger particles than clay, 

 as may easily be seen in the experiments just described : 

 the diameter of the particles ranges from .00004 inch 

 to .001 inch and larger. Sandy soils are usually called 

 "light" because they are more easy to work, although 

 a cubic foot of dry sand weighs one hundred and five to 

 one hundred and ten pounds, while a cubic foot of dry 

 clay weighs only seventy to eighty pounds. Test this 

 statement. They are more open, more porous, warmer 

 and drier than clay soils. Pure sand contains practi- 

 cally no plant -food ; it comes from quartz rocks ; the 

 purest sand consists of practically nothing but particles 

 of quartz which have a very characteristic appearance 

 under the microscope. In order to examine sand micro- 

 scopically, breathe on a slide, place a little sand on it 

 and then turn it up edgewise so that all the sand falls 

 off, with the exception of a few .scattered grains which 

 adhere to it. Examine in the ordinary way with the 

 aid of the mirror, giving a bright background, and also 



