58 ELEMENTARY AGRICULTURE 



they will be raised out of the ground as they increase 

 in length. All that has been said about cultivation of 

 plants applies with special force to root crops. 



How Water Rises in Soil. Another important 

 reason for cultivation is to be found in the fact that 

 cultivated soils do not dry out so rapidly during a 

 drought. This seems strange at first, but it is never- 

 theless tri.e, and the reason is easily seen. There 

 are two kinds of water in the ground capillary water 

 and "free," underground, water. Underground water 

 flows along beneath the surface and sometimes comes 

 out again in the form of springs. It is this water 

 that supplies our wells. But it is the capillary water, 

 and not the "free" water, that is used by the plants. 

 A simple illustration will make clear what capillary 

 water is. You have, no doubt, observed how oil rises 

 in the lamp-wick. The oil in the wick is moving 

 upward and may be called "capillary" oil, while that 

 in the lamp is "free." The oil in the wick corre- 

 sponds to the capillary water in the soil, while that 

 in the lamp corresponds to the underground water. 

 Another illustration: At the breakfast table take a 

 spoonful of sugar and just touch the tip of the spoon 

 to the surface of the coffee in your cup, and notice 

 how the coffee creeps up into the sugar. It is in 

 exactly the same way that the underground water 

 creeps upward in the soil and becomes capillary water. 

 Still another illustration : Fill a pan half full of 

 water: set it on a table and throw a rag over the edge 

 so that one end will dip into the water and the other 



