Draining 



bottom ; while with a clay subsoil they 

 resemble those of a pot without any opening. 

 In the former case the superabundant water 

 flows away and the air comes in ; in the latter 

 it must remain and the air cannot reach the 

 roots. 



Now we will consider marshy ground. On 

 account of the stagnant water, either on the 

 surface or at a slight depth below, nothing 

 can grow except a few hardy plants, such as 

 reeds, destined by nature to live in such 

 situations. Small trenches are dug at a depth 

 which cannot be reached by the roots ; a layer 

 of stones is placed at the bottom of these and 

 they are then filled up with the earth that has 

 been excavated. These trenches, hidden 

 underground, slope downwards, and at their 

 lowest point end in a main channel. The 

 water with which the ground is saturated 

 collects in these trenches, flows through the 

 bed of stones and falls into the main channel, 

 which carries it to some stream at a distance. 

 Now our marshy ground resembles the flower- 

 pot with its hole at the bottom, its frag- 

 ment of earthenware and its layer of gravel ; 

 the air can penetrate into it and cause it 

 to become fertile. This operation is called 

 draining. 



189 



