84 Science of Plant Life 



and water are formed. In photosynthesis, the energy of the 

 sunhght is used in building up the carbohydrates. The 

 energy is stored in the carbohydrates, and it may be released 

 by changing them back to the simple substances out of which 

 they were made. When we w^ind up a clock spring, we put 

 energy into the tightened coil. When the spring is allowed 

 to uncoil, this energy is released and turns the wheels of the 

 clock. So in photosynthesis the energy is stored in the car- 

 bohydrates, and this energy is released in the process of res- 

 piration and used in the life processes of the cell. 



In photosynthesis In respiration 



Oxygen is released. Oxygen is consumed. 



Energy is accumulated. Energy is released. 



Simple molecules are built up Complex molecules are broken 



into complex ones. down into simple ones. 



Plants accumulate food and Plants consume food and de- 

 increase in weight. crease in weight. 



Comparative rates of respiration. The rate of respiration 

 is greatest where there is rapid growth, as in germinating 

 seeds, opening flowers, and ripening fruits. In some of these 

 it is much more rapid, bulk for bulk, than in animals. The 

 lowest rates of respiration occur in seeds and other dormant 

 structures ; and there is comparatively little respiration in 

 woody stems and other hard parts in which there are oilly a ' 

 few living cells. 



Respiration and the shipping of fruits and vegetables. How 

 important the recognition of the respiratory requirement of 

 living cells is, may be illustrated by the difliculties that have 

 been met with in shipping fruits and bulbs. Peaches, during 

 shipment, sometimes develop brownish spots where they 



