244 BOTANY part i 



different organs and under various external conditions. Actively 

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

 and esj)ecially 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 because the carbon dioxide which is 

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

 of the sugar which serves as the material for respiration. The mole- 

 cule of sugar breaks down and forms, in addition to carbon dioxide, 

 other reduced compounds. It may be said that this kind of respiration 

 depends on the withdrawal of combined oxygen from one group of 

 the sugar molecule and its combination with other groups. Very 

 often alcohol or other reduced compounds are thus formed. 



Some seeds can remain alive for many hours or days with intra- 

 molecular respiration, and some even continue to give off the same 

 amount of carl)on dioxide as in ordinary respiration. In most cases, 

 however, the amount of CO^ rapidly diminishes. In other plants 

 death soon occurs, probably owing to the reduced compounds acting as 

 poisons. The value of intramolecular respiration is in these cases oidy 

 slight. On the other hand it has a very great importance in certain 

 organisms which will 1>e referred to later. 



