456 Irrigation and Drainage 



plete mat of fine fibers, which will fill the whole drain 

 and by arresting the silt moving with the water, com- 

 pletely closes it. In Fig. 144 are shown two bundles 

 of roots of the European larch which entered and 

 completely choked a 6 -inch main lying 5 feet below 

 the surface, and where the trees were standing 15 feet 

 away from the line. There are but few trees that 

 will grow in such places which can be trusted near 

 the drain, but the willow, elm, larch or tamarack, and 

 soft maple are among the worst. It should be under- 

 stood that so long as the water in the drain is flowing 

 it is highly charged with air, and trees may even bet- 

 ter immerse their roots in this than in the more 

 stationary water between the soil grains, hence they 

 do so wherever opportunity is offered, unless the water 

 should be poisonous. 



LAYING OUT SYSTEMS OF DRAINS 



In preparing to drain a piece of ground of con- 

 siderable extent, careful study should always be given 

 to the best way of laying out the system so as to 

 secure the greatest fall and the most complete drain- 

 age with the least digging and the smallest number 

 of feet of tile at the lowest cost. To do this, care 

 must be taken to avoid laying the lines so as to 

 bring their influence within territory already sufficiently 

 drained by another line ; to make the outlets and 

 junctions as few as possible ; to avoid the necessity 

 of the more expensive large sizes of tiles, and of dig- 

 ging more deeply than is required for good drainage. 



