SOIL AND WATER 99 



and their quantity be in the inverse ratio to the resistance 

 of the path or paths. It follows, therefore, that if e very- 

 portion of the soil — or those depths which are reached by 

 the roots of plants — is to receive the same current supply 

 it must not only have exactly the same conductivity but 

 must not be shut off by a fault, or break of continuity, such 

 as those described by Dr. Russell. 



We may be sure, quite sure, that in the absence of manure 

 or fertilisers, electrolytes are neither equally distributed 

 throughout the soil nor of uniform resistance, so that elec- 

 trification of the soil cannot be everywhere the same. When 

 a " fault " of the nature we have been discussing occurs 

 the pocket, so to speak, of soil would, presumably, be cut 

 off from the earth supply, or alternatively receive a 

 diminished supply owing to the resistance of the rock, and 

 be mainly dependent upon the atmosphere for its charge. 

 This, with a dry upper stratum would, in the absence of 

 rain, be negligible. It would appear, therefore, to be 

 desirable to test soils both for E.M.F. and sign of current 

 — to determine the nature of the charge — and where there 

 is a deficiency to arrange for a constant supply at a voltage 

 not materially higher than that of the earth. 



When the underlying rock is at a depth permitting of 

 root expansion a simple remedy might be to drive a metal 

 rod or tube through it to enable the earth current to pass. 



The Dicker soil lies on a deep bed of stiff clay. It is 

 wet in winter, when cold renders the soil practically non- 

 conductive, and parched in summer when drjTiess has an 

 even worse effect ; while in the case of the Shopwyke soil 

 the conditions repeat themselves, dry soil prevailing during 

 the summer months. 



From an electrical standpoint too much importance 

 cannot be attached to temperature, within certain limits, 

 in its relation to soil conditions. In warm damp weather 

 conductivity is at its maximum. Cold increases resistance 

 especially of liquid and semi-liquid conductors enormously, 

 and consequently lowers the quantity of current supply, 

 not only to the roots but in its circulation through the 

 vegetable organism. 



