SUB-IRRIGATION FOR LETTUCE. 



75 



alternate the plots. This, however, cannot be extended 

 very far, as the difference in heat in the two ends of a house 

 is considerable. A very good plan is to take a section of a 

 bed in the middle of a house and treat by one method of 

 watering, while two sections of the same size on either side 

 are treated according to the other method. This has been 

 done in several cases, and some examples are given in the 

 third table. In these experiments, the plants were treated 

 in the same manner as those in the experiments above men- 

 tioned, /'. e., all were sub-irrigated until they were planted 

 in the benches. After that time sections A and C were sub- 

 irrigated, and section B was surface-watered. The average 

 gain of the sub-irrigated plots over the surface-watered was 

 about 38 per cent, or very nearly the same as the average 

 of the 15 experiments in the second table. 



COMPARISON OF SURFACE-WATERED SECTIONS WITH SUB- 

 IRRIGATED SECTIONS ON EITHER SIDE, 75 GRAND 

 RAPIDS PLANTS IN EACH SECTION. 



" In all of the experiments thus far referred to, but 

 one point has been considered, and that is the increase in 

 weight by sub-irrigation. Aside from the relative preva- 

 lency of disease in plants treated by the two methods, there 

 are but few practical questions. 



"Although not a matter of much practical importance, 

 some interest attaches to the fact that sub-irrigated lettuce 

 is earlier than that grown in the ordinary manner. It does 

 not really come to maturity any earlier if by that is meant 

 the stage at which the plants cease to increase in weight, 



