SUBIRRIGATION AND SUBSOILING. 



431 



all surplus to drain off when a sufficient time has been 

 given the soil to take up the needed water. In this 

 way the soil can also be well aerated, and if bottom 

 heat is desired, one has only to run steam or hot water 

 pipes through the tiles. 



When the beds are to be irrigated, water is poured 

 quickly into the ends of the rows of the tiles, so that 

 it will run the entire length of each row at once, and 



FIG. 109 — GREENHOUSE IRRIGATION. 



soak out slowly and uniformly through the adjacent 

 soil; watering is to be done as often as the plants re- 

 quire it, and their needs are learned in the same man- 

 ner as by surface watering, but the applications need 

 not be so frequent as by the old plan. It may readily 

 be seen that this system has some advantages. Here- 

 tofore the difficulty has been that when the moisture 

 was applied dire(5lly on the plants, the result was rot or 

 mildew, lettuce being attacked by fungus severely in 



