184 



THE IRRIGATION AGE. 



the water until it soaks away among the inclosed plants a garden 

 modification of the rectangular check system; 



(5) Ridge irrigation, in which plants are grown on the sides or 

 at the bases of raised ditches a simple form of depressed-bed irri- 

 gation. 



(6) Furrow flowing, or running water in one or more furrows be- 

 tween the rows of crops grown in that way. 



(7) Raised-bed irrigation, in which the water is taken by seepage 

 and capillary action from a small ditch on each side a modification of 

 the furrow system . 



(8) Subirrigation; or distribution by means of pipes wilh suita- 

 ble outlets, or from blind ditches filled with material permitting cir- 

 culation of water which will reach the plant roots by capillary action. 



(9 Underflow irrigation, by which the ground water is raised by 

 percolation from ditches at intervals of considerable distance the 

 plant roots being reached directly or by capillary movement. 



(10) Distribution under pressure in underground pipes, with 

 stand-pipes and connections for sprinkling. 



FREE FLOODING. 



Free flooding is the oldest and simplest form of field irrigation 

 and consists in turning water out upon the land with only the inci- 



Fig. 12. Irrigation of a grain field by free flooding, showing cloth dam in position. 



dental restraint of the banks of the ditches, from which it is released 

 usually by spade cuts at intervals, or by overflowing the banks them- 



