80 EXPERIMENTAL PLANT PHYSIOLOGY 



The equation that represents the building up of starch 

 was given on page 68 : 



Water + carbon-dioxide + energy = Starch+ oxygen. 



The following equation may now be compared with " 

 the above : 



Starch + oxygen = Water + carbon-dioxide + energy. 



This equation represents the destructive action of 

 oxygen on starch. 



The first equation shows the assimilation or building- 

 up process for which energy must be supplied. The 

 second equation is that of respiration or breaking-down 

 in which energy is liberated. 



Summary. — The main facts that have been learnt 

 concerning the relation between the plant and the sur- 

 rounding air may now be tabulated. 



Air is used by the plant in connection with the 

 processes of feeding (carbon-assimilation) and breathing 

 (respiration). 



Carbon^assimilation. Resjilra tion. 



Carbon-dioxide is taken in. Oxygen is taken in. 

 Oxygen is given out. Carbon-dioxide is given 



out. 

 The air is purified. The air is rendered im- 



pure. 

 Only green parts of plants Every part of the plant 

 can use carbon-dioxide for breathes, 

 food. 

 Energy is required, there- Energyis set free, there- 

 fore carbon -assimilation fore respiration takes 

 takes place only in sun- place always, in dark- 

 light, ness as well as in the 



light. 



