THE POTATO 31 



are the farther apart they may be. Four rods is 

 a common interval in clay subsoils and eight rods 

 in open subsoils. In muck or peat it is frequently 

 best to put them eight rods apart at first, and if 

 that does not prove to be close enough together 

 an intermediate line may be put in later in each 

 space, making them eventually four rods apart. 

 In rare cases of springy soils it has been found 

 necessary to have lines of tile two rods apart. 



"A single line of tile in a wet sag is frequently 

 sufficient, but if more than four rods wide, two 

 lines are better, each to be located as near to its 

 side of the sag as seems necessary. In this way 

 the centre of the sag, unless it is exceedingly low, 

 will be protected from the seepage of the adja- 

 cent upland. 



"Mains are generally located parallel to a nat- 

 ural water course a little to one side if there is 

 danger of washing by the surface runoff. Sub- 

 mains should be so laid out as to give the lat- 

 erals a sufficient gradient without an excessive 

 depth. 



"Instead of permitting each lateral to dis- 

 charge directly into the outlet ditch, it is best to 

 put in a main perhaps four rods away from the 

 ditch and parallel to it, to receive the discharge 

 from the laterals. The expense is but little 

 greater because of the saving in the length of 

 the laterals, and there is an advantage in having 

 only one outlet that of the main to look 

 after. 



"The water in an outlet ditch should be enough 

 below the banks to afford an outlet for a line of 

 tile which may be laid to it from any part of the 

 marsh of which the ditch is the direct outlet. This 

 line of tile is entitled to a depth of 3 feet at the 



