NUTRITION AND SEASONAL LIFE OP PLANTS 121 



In the burning of wood the cellulose of the wood-cell walls 

 and. the stored sugar, starches, and nitrogenous foods are chem- 

 ically more complex than coal. As a consequence of this com- 

 plex chemical character of the substances oxidized or burned 

 the final products are more complex than in the burning of coal, 

 and iii addition to the energy released we have also carbon 

 dioxide, water, and other substances given off or thrown down 

 as by-products. In a somewhat similar manner we may picture 

 the respiration or oxidation processes which go on in the living 

 cells of germinating seeds or in other active cells of the plant 

 body of a growing plant. This combustion of more complex 

 compounds may also be represented by a generalized formula 

 as follows : 



Sugar 4- oxygen = carbon dioxide + water + energy 

 (C 6 H 12 6 ) 6 (0 2 ) 6 (C0 2 ) 6 (H 2 0) 



In the living cells of plants the compounds which are finally 

 oxidized are very complex and therefore yield more complex 

 final products than is the case in the oxidation of coal or wood. 

 Some investigators believe that the sugars and similar, substances 

 are directly oxidized in living cells, much as they-are in a piece 

 of wood containing these substances as reserve foods or as con- 

 stituents of cell walls. Others suppose that the protoplasm, or 

 living substance, is gradually decomposed during the respiratory 

 process and that oxygen plays an important part in the process, 

 which results in the release of energy and in the production of 

 carbon dioxide, water, and nitrogenous wastes ; for example : 



Proteins 4- oxygen .= carbon dioxide 4- water 



-f nitrogenous wastes 

 4- energy 



It appears, therefore, that while the energy released is com- 

 parable in combustion and respiration, the final waste products 

 are more elaborate in the oxidations which take place in living 

 cells than they are in ordinary combustion, for the reason that 

 more complex compounds, possibly including protoplasm itself, 

 are decomposed and partially oxidized in plant respiration. 



