io6 RELATIONS OF SOIL TO WATER 



hygroscopic water which it is capable of holding. This redis- 

 tribution of water will take place more easily when the loss is 

 occasioned by means of roots, because in this case the whole 

 action is beneath the surface, and the soil particles never 

 become perfectly dry. When perfectly dried and coated with 

 air, the renewal of a film of water becomes more difficult. It 

 is evident that this redistribution of water in the soil will be 

 effected to a greater extent (because more easily) by bringing 

 a fresh supply of water from above, or from the side, than 

 from below ; indeed in the case of coarse sands, the supply 

 from bolow must be extremely small. 



The case of a silt or loam is quite different ; here, when 

 percolation has ceased, the soil may remain nearly saturated 

 with water throughout its whole depth. When this condition 

 of equilibrium is disturbed, the movements of soil-water re- 

 establishing it will at first be far more vigorous than in the 

 previous case, the passages in the soil being in this case more 

 or less filled with water. The facilities for procuring a con- 

 siderable supply of water from below, will in this case be 

 largely increased. The advantages mentioned do not however 

 continue to increase as the size of the soil particles diminishes ; 

 we have in fact already pointed out (pp. 86, 97) that excessive 

 fineness of particles, while increasing the water-holding power 

 of a soil, greatly diminishes the freedom of movement of the 

 soil water. Stiff clay soils, when in a puddled condition, 

 notwithstanding the large amount of water they may contain, 

 are quite incapable of efficiently supplying the wants of a 

 plant ; the roots take water from the soil they are in con- 

 tact with, but this water is replaced so slowly from the 

 surrounding soil that the plant may die of drought. The 

 maximum advantages of capillary action are apparently to be 



