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- 
Fic. 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 
