RESPIEATION— AERATION— FERMENTATION 223 



tory processes of catabolism whicli go on in every active plant 

 and animal cjell. We have already learned that catabolism is a 

 destmctive pirooese. which must result in loss of weight and 

 energy unless the anabolic activities are greater than the cata- 

 bolic activities. Growth and both internal and external activity 

 of the cells are evidences of respiration. It always r^ults in 

 the talcing in of oxygen and the giving off of carbon dioxide. In 

 the germination of seeds the absorption of oxygen is greater 

 than the elimination of carbon dioxide, but in the actively grow- 

 ing green plant this ratio is reversed. 



Respiration and Germination. — We have learned that res- 

 piration occurs in the protoplasm of the living cell and that it 

 is most active during the period of greatest growth. Therefore, 

 we will expect the respiration processes to be very active during 

 the period of seed germination and seedling growth. In fact, 

 during the period of germination the plant requires much more 

 oxygen and gives off much more carbon dioxide in proportion 

 to its size than at any other period in the growth of the plant. 

 During this period of very great activity, the temperature may 

 be 10 degrees C. or even 20 degrees C. higher than the sur- 

 rounding atmosphere. 



During the period of germination the plant has little or no 

 chlorophyll, and, therefore, uses but very little or none of the 

 carbon dioxide for photosynthesis. It is living and growing on 

 the reserve food, must use oxygen and must give off carbon 

 dioxide. With the development of the chlorophyll it performs 

 photosynthetic work and builds tissues. 



Diffusion and Absorption of Oxygen. — Since oxygen is one 

 of the free gaseous elements of the air, it must necessarily pass 

 by diffusion into the stomata, where it comes in contact with 



