CULTIVATION. 



109 



by drains underneath, falling rain, instead of flowing 

 -away, filters through the soil, and, except in case of loose 

 Sand or gravel, leaves its fertilizing elements behind. 



4. It prevents the injurious effects of a drought. 



In a time of drought, while the surface soil becomes 

 very dry, there is generally sufficient moisture below. If 

 the lower portions have 

 been previously satu- 

 rated so as to prevent 

 roots from occupying 

 them, the plant is now 

 unable to obtain a sup- 

 ply of moisture, as its 

 roots are surrounded 

 with the dry surface 

 soil ; but if the surplus 

 water has been drained 

 away, so that the roots 

 have been able to make 

 their way downward, 

 when a drought occurs 

 the plant may obtain 

 its moisture through 

 these lower roots. 



5. It renders ivet land available for tillage. 



It is often the case that the wet lands upon the farm 

 are the richest in plant food. Many low, wet places con- 

 tain an accumulation of vegetable mold, and other fer- 

 tile matter washed in from the land around them. By 

 draining the water out of these places, we render them 

 permanent sources of wealth. 



Some farms are split up into small, irregular plots, by 

 narrow tracts of land, too wet for tillage. By draining 



Effect of Underdrainage. 



A, Drain-pipe. J?, Point below which the soil is 

 usually saturated. C t Point to which the water 

 settles in a dry time. 



