SUB-IRRIGATION FOR LETTUCE. 



73 



houses where the moisture in the air, in addition to the 

 normal quantity, comes almost wholly from plant tran- 

 spiration. 



"In the following table, the results with a number of 

 varieties are given. This was not intended as a variety 

 experiment, as those in the list are not comparable in the 

 manner presented, since some are varieties which form 

 heads while others do not. All that it is intended to 

 show is the relative development of each variety by the 

 two methods of watering. In this experiment each lot is 

 carried through the entire season of growth by the method 

 indicated. That is, the sub-irrigated plants were treated 

 in that manner from the time the seed was sown until 

 the crop was harvested. The surface-watered plants, on 

 the other hand, were surface-watered during their entire 

 season of growth. This is referred to particularly be- 

 cause it is not the plan which has been followed in the 

 greater number of our experiments. It will be seen that 

 the average gain in favor of the sub-irrigated plots was 

 about loo per cent. 



THE RESULTS OF SURFACE- AND SUB-IRRIGATION WITH 

 TEN VARIETIES OF LETTUCE. 



"In the next table, the separate results of 15 ex- 



