IRRIGATION 



241 



satisfactorily on a* water pressure of from 

 10 to 30 pounds. 



When constructing benches for sub-irriga- 



Fig. 126. Greenhouse bench arranged for sub-irrigation. 

 A, cement troughs on bottom of bench; B, drain tile or 

 perforated pipes for supplying water; C, drainage spaces 

 between troughs. 



tion, the essentials are a water-tight bottom, 

 usually of cement, to prevent the water from 

 leaking through, and perforated pipes or tiles 

 for distributing it along the bench. This 

 system has been tried out extensively with 

 varying results by the Ohio experiment 

 station. 



