THE CONTROL OF SOIL-MOISTURE 



215 



should be well protected, so that the end tiles may not be 

 loosened and the whole system endangered by clogging with 

 sediment. It is well to embed the end tile in a masonry or 

 concrete wall. The last eight or ten feet of tile may even be 

 replaced by a galvanized iron pipe or with sewer tile, thus 



^j i 



H, 



Fig. 39. — Gridiron and fishbone systems for laying tile drains. 



insuring against damage by frost. The water should flow 

 freely from a tile drain system, as a drowned outlet inter- 

 feres with efficient drainage. The opening of a tile drain sys- 

 tem is usually protected by a gate or by wire in such a man- 

 ner as to allow the water to flow out freely but preventing 

 rodents from entering in dry weather. (See Fig. 40.) 



As with any other improvement, tile drainage must be made 



