INTRODUCTION 41 



7. Respiration. 



Like animals, plants need to respire, or to make 

 use of the oxygen of the atmosphere, or water in the 

 case of submerged aquatic plants, and ground air 

 between particles of soil at the roots in the case of 

 land-plants. 



By means of respiration or oxidation the oxygen 

 in the atmosphere is utilised and combines with 

 carbon, so that carbon dioxide is set free and the 

 oxygen is utilised or circulated. This is somewhat 

 the reverse of the process of the carbon assimilation 

 or deoxidation to be considered next. In the latter 

 substance is gained, in the former gas is lost. In 

 the former energy is locked up or potential, in the 

 latter it is set free or converted into kinetic energy. 

 The oxygen acts on the organic substances formed as 

 food, and breaks them down by a process of katabolism 

 in place of a building-up or anabolism. The work 

 performed in the latter process must be translated 

 into energy. In other w^ords, the process or result 

 of nutrition is of no use to the plant without a corre- 

 sponding growth. 



Every cell takes part in the process of respiration. 

 This is facilitated by the existence of stomata, by 

 which the air enters, and by the intercellular spaces 

 into which such gases are passed, and then into the 

 cells, where the gas is dissolved in the cell-sap, 

 entering into combination with the carbohydrates. 



