AMOUNT OF MOISTURE RETAINED BY PLANTS 19 



Discussion: We have already found that a large part 

 of the water taken up by the roots is evaporated from the 

 leaves of the plant, leaving behind tne food material which 

 it carried in solution from the soil. We now see that a 

 sufficient amount of water is retained to make up a large 

 percentage of the total green weight of the plant. This 

 moisture gives rigidity to the plant. When the loss by 

 evaporation from the leaf surface is more rapid than the 

 water can be supplied from the soil, the plant soon wilts 

 and ceases to grow. It has been found that our ordinary 

 plants take up from 300 to 500 pounds of water for every 

 pound of dry matter produced by them. 



From an experiment in New York State it was found 

 that a field of oats used 522 pounds of water for each pound 

 of dry matter produced; corn 234 pounds; and potatoes 

 423 pounds. 



The evaporation of the water from the surface of the 

 leaf is known as transpiration. 



In addition to the large amount of water which leaves 

 the soil through the plant, there is a constant loss of water 

 by direct evaporation from the surface of the soil. 



