CHAPTER VIII 

 INTAKE AND DISTRIBUTION OF GASES 



Oxygen and Carbon Dioxide Necessary to Plants. All 



plants liberate energy stored in complex compounds, and all 

 of the higher plants and most of the lower need the free oxy- 

 gen of the atmosphere to do this fast enough for their normal 

 functions. The union of free oxygen with the protoplasm 

 and .reserve foods whereby these substances are broken down, 

 and in consequence energy is liberated within the cells, is the 

 essential process of aerobic respiration, while in anaerobic res- 

 piration the breaking down process releases energy without 

 the assistance of oxygen. This energy is used in keeping up 

 the vital processes. Respiration, in other words, is the means 

 of converting stored or potential energy into active or kinetic 

 energy. This is the essential function of respiration without 

 which plants could not live any more than animals could. Each 

 living cell of the plant body must respire for itself, for the en- 

 ergy liberated in one cell is' not available in the next. We are 

 led to conclude, indeed, that any part of the living protoplasm 

 that is to benefit by the kinetic energy must take part in its lib- 

 eration and be directly acted upon by the kinetic energy as it 

 is being transformed from the potential condition. In a large 

 plant body, therefore, consisting of masses of cells, there must 

 be provision for access of oxygen to every cell, and for the elimi- 

 nation of carbon dioxide resulting from respiration. The 

 oxygen absorbed by one cell may diffuse into one adjoining; 

 and so on for a short distance; but the surest way of securing 

 to each cell all of the oxygen that its greatest demands may 

 require is to have it exposed for a part of its surface to an air- 

 carrying intercellular space, a condition that is approximated 

 by an elaborate system of intercellular spaces. 



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