PLANT PHYSIOLOGY 



135 



PHOTOSYNTHESIS AND METASTASIS CONTRASTED 



The relation between these two functions of plant life may 

 be better understood by the following contrast: 



PHOTOSYNTHESIS 

 Takes place only in green cells. 

 Takes place only in light. 



C0 2 is absorbed and used up 

 and oxygen given off. 



Carbohydrates are formed. 

 The plants grow in weight. 



The energy of sunlight is stored ; 

 see Chapter XV. 



METASTASIS 

 Takes place in all living cells. 



Takes place equally well in 

 darkness. 



Oxygen is absorbed and used 

 and CO 2 given off. 



Carbohydrates are destroyed. 



The plants lose weight, but may 

 increase in size. 



The stored energy of sunlight is 

 liberated and used. 



The forces concerned in starch making and the building of 

 proteids and other materials are ordinary chemical and physical 

 forces. While we cannot cause these particular chemical com- 

 binations to occur in our laboratories, and do not understand 

 them fully, we do know enough about them to prove that they 

 belong to the ordinary forces of chemical affinity. In starch 

 making the atoms are combined in ordinary proportions, and 

 there is no reason for thinking that any other factors are con- 

 cerned besides those of chemical affinity. 



MISCELLANEOUS FUNCTIONS OF PLANT LIFE 



Besides the processes of photosynthesis and metastasis, the 

 only other prominent function of plant life is reproduction. 

 The two functions of motion and coordination, which are very 

 prominent in animal forms, are very slightly developed among 

 plants. 



