FORCING AND FORCING STRUCTURES 8 1 



level along the lines where plants are to stand. If the bench is 

 capable of carrying 5 rows of lettuce, a line of pipe should be 

 placed under each row, the joints of the pipe being cemented so 

 as to make a trough which will hold water, as shown in figure 26. 

 The trough should then be filled with coarse gravel or clinkers, and 

 an upright provided to admit water. Bricks should be placed be- 

 tween the lines of tile, and the bench filled with soil in the ordinary 

 manner. This will be found an efficient means of subirrigation. 

 This construction is quite expensive but it is durable and efficient. 

 If the moisture in the soil is to be maintained by surface water- 

 ing, care should be exercised to thoroughly wet the soil and not 

 repeat the operation until the plants indicate that water is again 

 needed. This is expressed by the plants assuming a slightly darker 

 green tint. Do not keep the soil saturated with water but do not 

 allow the plants to flag before watering again. In hot weather 

 much can be done to safeguard the plants by wetting the walks. 



