62 SUNLIGHT AND PLANT GROWTH 



other elements taken from the soil, and is finally con- 

 verted into the actual substances of which plants are 

 composed. 



Photosynthesis. - - This process of making sugar 

 which takes place in the leaves during sunlight is called 

 photosynthesis. Carbon dioxide, which is taken from 

 the air into the leaves, is a gas composed of carbon and 

 oxygen ; and since only the carbon is used in the 



COMMON FORM OF MOLD (magnified) 



process of photosynthesis, the oxygen is liberated and 

 expelled into the air. This process of taking in carbon 

 dioxide and throwing off the oxygen must not be con- 

 fused with respiration of plants. Respiration goes on 

 in plants as it does in animals. Both plants and ani- 

 mals in breathing take in oxygen from the air and 

 expel carbon dioxide. But during the life of a plant 

 more oxygen is given off to the air by photosynthesis 

 than is taken from the air by respiration. 



