THE SOIL AND SOIL FORMATION 



79 



Figure 26. Pot of soil 



oiSed dra and ' 



the level of the spout. The soil will still be very moist, 

 but, if placed in the dry air of a living room, the drying 

 action of the air will soon remove some of this excess 

 by evaporating moisture from the surface particles. 

 These, in turn, will be given some of the capillary mois- 

 ture from the particles next below. Thus there will be 

 a slow, upward flow of moisture, sim- 

 ilar to the upward movement of oil in 

 a lamp wick, or to the upward move- 

 ment of water into which the lower 

 part of a sponge is inserted. If the 

 ground water is sufficiently near the 

 surface, it will be a source of moisture, 



1 



kee P m g th e soil and subsoil partially 

 saturated with capillary water, thus 

 providing the crops with a constant 



supply of water. In Figure 26 the water in the bottom 



of the pot not drained out, because the drain at B re- 



mains closed, will be a permanent source of capillary 



water to the upper soil, to renew that taken up by 



evaporation from the surface of the soil 



into the air above, or that absorbed by 



plant roots growing throughout the 



upper portion of the soil. The air 



within the soil is kept very moist by the 



evaporation which takes place from the 



r _ M . 



many moist surfaces. This watery 



vapor in the soil air diffuses outwardly 



into the atmosphere above, aided some- 



what by the slight circulation of air into wat( 



and out of the soil, thus causing some loss of moisture 



which does not pass off through the plant. These losses 



will gradually use up all the ground water held below the 



upper drain, Figure 26, and leave the soil with only 



capillary water, as in Figure 27. The soil filled only with 



capillary water, as in Figure 27, is also gradually dried 



Figure 27. Tot of sat- 



SteM>eSS A'hS b! 



