I04 The Great World's Farm 



water so far beneath as to be quite beyond the reach of 

 their roots? The answer to which is that it does not 

 remain beyond their reach, but is brought up to them. 



The water in the soil, visible or invisible, is like a 

 stream which is never at rest; it is in constant motion, 

 always either rising or sinking according as the surface of 

 the soil is damp or dry. 



When the surface is wet from rain, the rain goes on 

 sinking down and down till it is either absorbed by the soil 

 through which it passes, or accumulates at some greater 

 or less depth below. But when the sun shines out again, 

 or a dry wind blows, the moisture of the surface is evapo- 

 rated, the upper soil grows dry again, and the moment it 

 is drier than the soil below, the damp soil begins to give 

 up its moisture to this drier bed immediately above it. 

 Thus the stream of moisture at once begins to ascend, 

 and will continue to ascend until the surface is wetted 

 again; it moves, in fact, either up or down, to the drier 

 parts of the soil, whichever these may be, the movement 

 being exactly like that of the oil in the wick of a lamp; as 

 fast as the oil is consumed, more rises to take its place. 



In time of drought the soil may appear quite dry even 

 to some depth, but as we have seen in the case of the 

 tobacco planted in sand, plants can continue to draw 

 moisture from the soil long after all trace of moisture has 

 vanished, so far as can be seen. To find it at all we 

 should have to dry the soil by artificial heat; but it is 

 there, and the plant manages to draw it out. 



In very long droughts, even the springs near the sur- 

 face may fail, all their water being drawn away from them 

 by degrees; but still, at a greater or less depth, some 

 water there is, for the deeper wells do not fail though 



