CHAPTER VI. 



RESPIRATION, DIGESTION, AND FERMENTATION. 



103. Release of energy — A large number of complex 

 substances are formed in the plant as "a result of photosyn- 

 thesis and other synthetic processes. All such construction 

 results in the storage of energy in a potential form, and the 

 food material acquired by the plant represents so much 

 potential which must be liberated to furnish energy for 

 growth, construction of organs, movements of the body, 

 movements of fluids in the body, and, in exchange with the 

 substratum and atmosphere, maintenance of position, and 

 rigidity of the body. The plant, therefore, only makes use 

 of its food material when it builds up tissues, or liberates the 

 energy which is held in the food. 



The liberation of energy is accomplished by respiration 

 and fermentation. Many types of respiration may be recog- 

 nized. In one of the best known forms, the material in liv- 

 ing matter is oxidized and carbon dioxide is set free, in exact 

 opposition to photosynthesis, which is a reducing process. 

 The proportions of the gas exchanged in respiration show the 

 greatest variation. In a modification of the above form of 

 respiration the oxidation is incomplete, and no carbon diox- 

 ide is liberated. In another method, respiration is effected 

 without the intervention of external oxygen. 



Energy may be released in the plant by fermentation, 

 by the action of a group of substances known as enzymes, 

 which have the power of inciting chemical changes in com- 

 pounds with which they are in contact, without entering into 



