Oct. 15, 1914 



Water Requirement of Plants 



from the sun was reduced about 20 per cent by the inclosure at midday 

 in midsummer, while total radiation measurements made with a differ- 

 ential telethermograph (Briggs, 191 3) gave approximately the same 

 reduction. Simultaneous measurements of the water requirement of 

 wheat, alfalfa, and cocklebur grown inside and outside the inclosure in 

 191 3 showed that the inclosure reduced the water requirement about 22 

 per cent. The water-requirement measurements must therefore be con- 

 sidered relative rather than absolute. In this connection it should be 

 recalled that plants growing under field conditions are also mutually 

 shaded and otherwise protected to some extent. -The writers' measure- 

 ments in 1 91 3 show that wheat grown in pots sunk in trenches and sur- 

 rounded by a field of grain has a water requirement 10 per cent above 

 wheat grown in the inclosure and 10 per cent below wheat grown outside 

 the inclosure in a freely exposed wind-swept position. (See Table I.) 

 The stand of wheat about the trench was below normal, owing to the dis- 

 turbance of the plants in trenching and in caring for the pots. The potted 

 plants in the trenches were consequently more exposed than if growing 

 normally in a field of grain. The water requirement of the potted plants 

 in the trench is therefore somewhat above that of plants normally pro- 

 tected. From this comparison it appears that the inclosure measure- 

 ments, at least in the case of wheat, are less than 10 per cent below the 

 water requirement of plants exposed under field conditions. 



