SOIL WATER 



137 



which tenaciously adhere to soil particles refusing to 

 be pressed or dried therefrom are called hygroscopic 

 water. This distinction aids in conceiving the func- 

 tions of tillage, for gravitational water is injurious 

 to all fruit trees, and unless removed by drainage 

 will surely "water-log" the land; hygroscopic wa- 

 ter is an inconsequential quantity too small to be 

 material, cultivated plants being entirely depend- 

 ent upon capillary water for growth. 



The power of a substance to absorb by capillarity 

 is seen by placing one end of a soft cloth, or blotter, 

 in liquid, the whole material soon becoming satur- 

 ated ; in soil this quality is most plain when brick, 

 or partially decayed wood, is buried, for moisture 

 continues therein long after the surrounding soil 

 has thoroughly dried. If spaces between soil parti- 

 cles are too large, as in coarse sand or gravel, capil- 

 larity is impaired, for water cannot remain sus- 

 pended between such particles by their attractive 

 action ; while if clay is so packed that the spaces 

 are closed, which ordinarily exist between the min- 

 ute particles, water percolates slowly by reason of 

 its impervious nature, and not from inability to at- 

 tract by capillarity. 



When the moisture content exceeds the capillary 

 capacity of the soil, the whole quantity becomes 

 gravitational, and is not in condition to maintain 

 plant life until the excess passes off. Our scientific 

 investigations have not shown if this result is due 



