THE DRAINAGE OF GRASS LAND 11 



crops upon it. Water would, after it has passed through the 

 surface to the subsoil, be lost to plant life, were it not for 

 the wonderful natural arrangement known as capillarity.^ As 

 the surface soil loses water by evaporation, it draws up 

 and reabsorbs moisture from below ; and this is especially 

 the case when the soil becomes dry, and its particles are 

 disintegrated. The water which is thus brought from the 

 subsoil contains in solution some of the mineral constituents 

 from the formation below, which further aid the growth of 

 plants. This fact accounts for the widely different gi'asses 

 which are to be seen in old pastures on surface soils that 

 appear to be identical. The mineral constituents in a state 

 of solution are brought up by the water from considerable 

 depths, and by this means, amongst others, the geological 

 substratum asserts its influence upon the herbage growing on 

 the surface. 



It is a mistake to suppose that the rainfall goes direct to 

 the drains and is at once expelled from the land. On the con- 

 trary, the rain sinks into the land until it meets and mingles 

 with the subsoil water, and the drains do not begin to run until 

 the subsoil water rises above their level. While water, how- 

 ever small the quantity, is flowing in a drain-pipe — and probably 

 long after it has ceased to flow — it may be taken for granted 

 that the subsoil is saturated with moisture up to the level of 

 the drains. The rise and fall of the subsoil water are therefore 

 determined by the level of the drain rather than by the surface 



^ Baron Liebig, in his Natural Laws of Husbandry, thus describes the action of 

 water in a state of motion : — 



' If we regard the porous earth as a system of capillary tubes, the condition which 

 must render them best suited for the growth of plants is unquestionably this : that 

 the narrow capillary spaces should be filled with water, the wide spaces with air, and 

 that all of them should be accessible to the atmosphere. In a moist soil of the kind 

 affording free access to atmospheric air, the absorbent root-fibres are in most intimate 

 contact with the earthy particles ; the outer surface of the root-fibres here may be 

 supposed to form the one, the porous earthy particles the other wall of a capillarv 

 vessel, the connection between them being effected by an extremely fine layer of 

 water.' 



