THE PHYSIOLOGY OF NUTRITION 



125 



by living plants and carbon dioxide given out both during 

 light and darkness. 



During assimilation the plant gains weight, but during active 

 respiration there is a loss of material. The loss is caused by 

 the oxygen uniting 

 with the carbon 

 compounds of the 

 plant to form carbon 

 dioxide. This loss 

 of weight due to 

 respiration supplies 

 the plant with 

 energy, by means 

 of which it is able 

 to assimilate. If 

 a plant which is 

 growin'g well be 

 placed in an atmo- 

 sphere of pure nitro- 

 gen, or hydrogen, or 

 in air from which 

 the oxygen has been 

 absorbed, the active 

 life of the plant 

 ceases at once. It 

 has been calculated 

 that one hour's as- 

 similation will 

 counterbalance 

 thirty hours' loss by 

 respiration. 



Heat is Pro- 

 duced by Respi- 

 ration. A ther- 

 mometer surround- 

 ed by germinating 

 seeds registers a 



FIG. 146. Experiment in respiration. B, an inverted 

 flask containing flowers, which are held in position 

 by cotton wool, W ; K, solution of caustic potash ; 

 Q, mercury, which rises in the neck of the flask, 

 because carbon dioxide is absorbed by the caustic 

 potash solution. (S.) 



rise of temperature. 



Flowers which are actively respiring produce both heat and 

 carbon dioxide. This can be shown by placing a number of 



