272 BOTANY PART i 



while, in typical respiration at least, the C0 2 formed during the night escapes, and 

 is lost to the plant. The succulents thus economise their supply of C, which is 

 probably connected with the fact that they do not so readily obtain carbon dioxide 

 from the air as other plants, owing to the diminution of gaseous exchange on account 

 of the limitation of transpiration. 



As has been mentioned, respiration is of general occurrence 

 in the higher plants. It not only occurs in the parts of plants which 

 do not possess chlorophyll and are commonly used in experiments 

 on respiration, but can be demonstrated also in cells which contain 

 chlorophyll. In this case the respiration in the light is masked by 

 the quantitatively greater process of assimilation ; it appears only as a 

 diminution in the products of assimilation. If the light is diminished 

 assimilation ultimately ceases and the respiration becomes evident. 



Though respiration goes on in every cell its intensity varies greatly 

 in different organs and under various external conditions. Actively- 

 growing parts of plants, young fungi, germinating seeds, flower-buds, 

 and especially the inflorescences of Araceae and Palms, exhibit very 

 active respiration. In some Bacteria and Fungi this exceeds, as 

 compared with the body-weight, the respiration of the human body. 

 In most cases, however, especially in parts of plants composed wholly 

 or mainly of full-grown tissues, the consumption of oxygen and 

 production of carbon dioxide is considerably less than in warm-blooded 

 animals. Among external conditions which have an important 

 influence on the intensity of respiration the temperature and the 

 amount of oxygen must be especially mentioned. An increase of 

 temperature accelerates respiration as it does all the vital processes. 

 The production of carbon dioxide is about doubled or trebled by a 

 rise of 10 C., just as other chemical processes outside the plant 

 are. With continued rise of temperature, however, the respiration 

 diminishes. In contrast to other like phenomena the fall in the 

 respiratory curve is exceedingly steep, so that the optimum and 

 maximum almost coincide. 



Respiration is commonly spoken of as a process of combustion. 

 Were this correct it might be .expected that the amount of available 

 oxygen would be of fundamental importance ; in particular it 

 might be anticipated that respiration would be greatly increased in 

 pure oxygen and completely suspended in a space free from oxygen. 

 Neither of these assumptions is true. Respiration is not markedly 

 increased in pure oxygen, and only at a pressure of 2-3 atmospheres 

 of oxygen does an increase in the respiration become perceptible ; 

 this is soon succeeded by a decrease in the respiration indicating the 

 approach of death. Even more striking is the fact that plants in the 

 absence of oxygen continue to produce carbon dioxide. In this case 

 one cannot speak of a process of combustion ; the phenomenon is termed 

 INTRAMOLECULAR RESPIRATION ( 45 ) because the carbon dioxide which is 

 formed owes its origin to a rearrangement of the atoms in the molecule 



