in] WATER SUPPLY 29 



reveals its true nature ; the rock, if thin enough, may 

 be broken or removed; but the thinly spread soil 

 on a gravel bed is beyond our present powers of 

 treatment. 



When the cultivator has any reason to doubt the 

 efficiency of the water supply to his plants he must 

 first ascertain whether the fault is in the soil or its 

 surroundings. The bad effects of too much clay may 

 be modified by liming, chalking, or drainage ; exces- 

 sive sand may be counteracted by additions of clay 

 or silt or by ploughing in organic manures and green 

 crops. In all cases the water supply is improved by 

 extending the range over which the roots may grow, 

 for the larger the volume of soil on which the plant 

 draws the less will be the amount of water required 

 from each portion. And so if any obstacle exists to 

 the development of the roots it must be removed; 

 the soil must be dug or ploughed more deeply and, 

 in a garden, manure must be added to the lower spit ; 

 any pan or thin rock layer must be broken up and 

 removed ; and stagnant soil water must be prevented 

 from rising too high by tapping the springs or by 

 laying deep drains 1 . A good deal can be done by 

 skilful cultivation to check evaporation and thus 

 reduce the loss of water. A fine layer of soil on the 

 surface effectually shields the rest of the soil from 

 the sun's heat and keeps the moisture safe from loss. 



1 See p. 78. 



