TILE DEAINAGE. 29 



It is a continuous process or growth from the bottom all 

 night long of loose porous ice. Incidentally it is well to say 

 that, as this hoar-frost lifts with it considerable amounts of 

 surface earth, therefore if clover seed be sown before it is 

 formed, then, when the frost thaws, the seed will usually be 

 nicely covered. 



The power of this stool-ice or hoar-frost is very great. If 

 it freezes around and partly under clover and wheat plants* 

 and roots, it will lift them perhaps half an inch each clear 

 frosty night. The sunshine of the next day thaws the frost 

 and leaves the roots lifted just so much ; and the next frost 

 will lift them more, and so on until they are out of ground, 

 or so nearly so as to have little vitality for growth. I have 

 seen many fields of wheat on damp undrained soil ruined in 

 this way ; and many fields of clover, with the great tap roots 

 sticking up into the air five or six inches all over the fields 

 in spring, like long numb fingers lifted toward heaven, and 

 crying for tile drainage ! for tile drainage almost wholly pre- 

 vents this by lowering the level of saturation, or hydrostatic 

 water, so much that only the smallest capillaries can pump 

 it to the surface. Or, aided by the warmth of the sun and 

 the action of the wind, it may even dry out a layer of earth 

 at the surface of the ground, so that this may act as a dry 

 mulch, or blanket, a non-conductor or poor conductor of 

 heat and cold between, the frost and the top ends of even the 

 smallest capillary pores, and thus nearly or quite thwart the 

 power of the cold atmosphere to form this stool-ice. 



These principles and facts throw light upon a curious and 

 hotly contested question in tillage ; viz., Shall we retain 

 moisture by cultivating the surface among "hoed crops" 

 immediately after showers in summer? " Yes," say the 

 careful, practical observers, "we know by frequent trials 

 that this really does help to retain moisture in the soil." 



" No," say those who have a mere smattering of science ; 

 " we stir hay with a tedder to make it dry faster ; and if we 

 stir the soil with a cultivator it will just make it dry faster." 



