UTILIZATION OF PLANT FOOD 35 



matter. It does not lose weight. Experiments have shown 

 that the material assimilated may amount to thirty times 

 that lost by respiration. 



27. Products of Respiration. The gases of respiration, 

 oxygen and carbon dioxide, can pass from cell to cell by 

 diffusion, being dissolved in water and transported like other 

 soluble compounds. The greater part of these gases, however, 

 exists in the intercellular spaces which have access to the 

 outer air through the stomata on the leaves, and the lenticels 

 in the bark and roots. The oxidation of material liberates 

 in the plant several forms of energy. First, heat is generated 

 to a noticeable extent in germinating seeds, flowers, and 

 buds, though for the most part it is dissipated by radiation, 

 plants having a much larger radiating surface in proportion 

 to their mass than do animals. Second, work results, such 

 as movements of various organs; of the entire plant; or 

 of protoplasm within the cells. Food is also transported. 

 Third, chemical energy is developed by the formation of 

 new compounds, by the solution of some, and by the pre- 

 cipitation of others. 



28. Intermolecular Respiration.— In addition to ordinary 

 respiration which takes place only in the presence of free 

 oxygen, there occurs, especially under conditions where 

 oxygen is wanting, a process of oxidation at the expense of 

 other molecules by their reduction. That is, energy for 

 certain processes may be derived by a reaction between 

 molecules in the same cell, resulting in the temporary 

 release of oxvgen from one of them. This mav be called 

 intermolecular respiration. The products of such oxidation 

 are, besides carbon dioxide and water, ethyl alcohol, higher 

 alcohols, acids, aromatic compounds, and even hydrogen. 

 This sort of oxidation, it must be remembered, means as 

 much reduction as oxidation. Where one molecule gains 

 an atom of oxygen another molecule loses it. Plant cells, 

 however, cannot live for any length of time by means of 

 intermolecular respiration alone. All crop plants must 

 have free oxygen for their development. 



29. Manufacture of Oil. — Particles or films of oil seem 

 to be a necessary constituent of plant cells and this material 



