FARM DRAINAGE. 57 



the chemical changes wrought upon it. Precisely this is accom- 

 plished in the soil by drainage; for, as we lower the water-line 

 and admit the air and warmth, this chemical action is induced. 



Still another way in which drainage deepens the soil is by 

 enabling the roots to penetrate the subsoil, and by their decay 

 they form humus, which is one of the most important ingredi- 

 ents of a fertile soil. The character and value of humus will 

 be* explained in another chapter. 



The fact is well known to every observant farmer that only 

 the sedges and coarser plants will flourish on a soil saturated 

 with water. The growth of flags, sedges, skunk cabbage, etc., 

 is one of the signs nature hangs out, like a flag of distress, to 

 show that the land needs to be drained. When such soils are 

 drained, these worthless plants die out, and are replaced by 

 those of value to the farmer. 



Underdraining makes the land warmer, by admitting the 

 warm air to the soil, for, as nature never allows a vacuum, as 

 fast as the water is drawn off, the air penetrates and warms the 

 soil. A dry soil is warmer than a wet one, because evaporation 

 is avoided. Science teaches us that the evaporation of one 

 pound of water requires more than five times as much heat 

 as would be needed to raise the same amount from the freezing 

 to the boiling point. We have many illustrations of the truth 

 of this, as, for example, the water in a jug will remain cool as 

 long as it is kept wrapped in wet flannel. Perspiration on the 

 body, by its evaporation, keeps us cool, and enables us to 

 endure heat that would soon be fatal if it were not for this 

 wise arrangement of Providence. 



If the water which falls upon a field must be removed by 

 evaporation, it is easy to see that the heat which otherwise 

 would warm the soil, and fit it for pushing the growth of 

 plants, must be expended in evaporating the water. 



Many tests have been made with the thermometer, and the 

 temperature of the drained field has been shown, during the 

 spring, to be several degrees higher than that of the undrained. 

 A drained soil can be plowed much earlier in the Spring than 

 an undrained one, and, as a loose soil admits sun and air, and 



