262 LEAVES 



hour, transpiration in greenhouses often drops to 10 grams or less 

 at night and rises to 50 and often to 100 or more grams during 

 the day. For plants outside where there is more exposure to 

 transpiration the variation is much greater. 



As compared with the dry weight produced, the amount of 

 water transpired by the plant is surprising. It has been esti- 



FIG. 237. Branch of a plant enclosed in a flask in which the air has 

 become so moist through transpiration from the enclosed leaves that mois- 

 ture has condensed on the flask. 



mated that in the Central United States about 425 pounds of 

 water are transpired for each pound of dry matter produced by 

 the plant. It is stated that for the production of one pound of 

 dry matter, Corn requires 272, Potatoes 423, Red Clover 453, 

 and Oats 557 pounds of water. Calculated on the same basis, 

 the production of one acre of Oats of average yield requires 945 

 tons of water. According to estimates, an Apple tree having 

 thirty years of growth may lose on an average of 250 pounds of 

 water per day, or possibly 18 tons of water during a growing 

 season. An orchard of 40 such trees would transpire about 700 

 tons in a season. It has been estimated that even an acre of 

 Grass may transpire from 500 to 700 tons of water during a 

 season. Now, if an orchard is in sod, then there is the loss of 



