50 



Science of Plant Life 



this vapor passes out into the atmosphere. The epidermis of 

 the leaf also allows some water to pass through it, but in land 

 plants this is a relatively small amount, because the cuticle 

 hinders the process (page 54) . The giving off of water vapor 



from plants is called transpiration. 



The loss of water in the form of 

 vapor is a process that takes place in 

 animals as well as in plants. If you 

 hold your hand near a windowpane 

 on a cool day, a halo of minute water 

 drops condenses on the glass. These 

 water particles come from the moist 

 cells of your skin. If you blow on 

 a glass, water collects even more 

 abundantly. The vapor in the 

 breath is water that has evaporated 

 from the moist cells of the lungs. 



The amount of water transpired 

 by plants. The amount of water 

 given off in transpiration is surpris- 

 ingly large. During its lifetime, a 

 well-watered corn plant may give off 

 4 or 5 gallons of water. A sunflower 

 plant may transpire more than 18 

 gallons. The water given off by a 

 field of wheat during its entire 

 period of development would cover 

 the field to a depth of 4 or 5 inches. 



scale.) In eastern Colorado the For the bcst growth of plants, there- 

 transpiration from a well-watered r jT. .1 •! 1 1 • j1 



com plant might be 3 times this ^o^^' there must be available m the 

 amount. soil enough water to permit them to 



Fig. 33. Corn plant, and bottle 

 of water equivalent to that tran- 

 spired by the plant during its Uf e- 

 time. (All drawn to the same 



