72 SOILS AND FERTILIZERS 



earth is clothed with living verdure. Generally stand- 

 ing water is found in the soil in large quantites, cither 

 deep in the ground, or, more rarely, near the surface. 

 This is called ground, or hydrostatic, water. When 

 found near the surface, ground water must be drained 

 off in order that vegetation may grow, because the 

 presence of so much water excludes the air from the 

 roots of the plant. When ground water exists at a 

 moderate depth, from three to four feet, it is helpful 

 to the plant, as it furnishes necessary moisture to the 

 soil above without excluding the air. 



The water that is most helpful to plant life is that 

 which surrounds each particle of soil in a thin layer, or 

 film. This is called capillary water. It does not fill 

 all the spaces between the particles and thus does not 

 shut out the necessary air, as does ground water. 

 Capillary water passes freely from particle to particle, 

 always from the more moist to the less moist, and thus 

 to the root tips, by a process which is known as cap- 

 illary action, or capillarity, the same process which 

 causes the whole of a linen towel to become wet al- 

 though only a small corner rests in water, or which 

 causes the oil to rise in a wick.. 



In dry weather capillarity will draw the ground water 

 up to the roots of plants and thus furnish necessary 

 moisture. Soils never become so dry that heating to a 

 temperature of 212 F. will not show the presence of 

 some moisture. This is known to the scientist as 

 hygroscopic water. It is absorbed from the air, as is 

 shown by the fact that the heated soil, when cold, will 

 regain the weight lost by heating. Hygroscopic water 

 clings to the surface of the soil particles, but is not 

 capable of movement as is capillary water. 



