300 VEGETABLE PHYSIOLOGY 



respiring plant is cut off from a supply of oxygen. Death 

 does not immediately supervene, as might almost be expected. 

 Instead, the partial asphyxiation or suffocation stimulates 

 the protoplasm to set up a new, and perhaps supplementary, 

 series of decompositions, resulting in the liberation of 

 energy, as do those of the respiratory process. We have 

 already noticed that under such circumstances the exhaling 

 stream of carbon dioxide can still be observed. This led 

 originally to the view that the protoplasm excited these 

 decompositions of some complex substance in the cell to 

 obtain oxygen from it, which should replace the oxygen 

 whose access had been stopped. The ultimate changes 

 were accordingly held to go on with but slight interruption, 

 but the source of the oxygen taking part in them was 

 different. On this account the process was termed intra- 

 molecular respiration. The term is rather an unfortunate 

 one, for, as we have seen, the study of the ordinary respira- 

 tory processes has shown that the molecule of the living 

 substance is the seat of the changes they involve, and hence 

 that all respiration is intra-molecular. Moreover if the 

 object of the decomposition is to provide oxygen to replace 

 that which has been cut off, these transformations precede 

 the actual respiration, which must then be set up as soon 

 as the oxygen is liberated as suggested. Many botanists 

 now prefer to speak of decompositions taking place in the 

 absence of a supply of free oxygen as anaerobic respiration. 

 They thus include as respiratory changes all the decomposi- 

 tions primarily intended to liberate energy, and divide them 

 into those which are aerobic or dependent on oxygen, and 

 those which are anaerobic. The latter need not involve 

 the co-operation of oxygen in the disruption of the molecule. 

 The object sought is energy and not oxygen. 



It is uncertain how far the self-decomposition of proto- 

 plasm is concerned in these anaerobic respiratory processes. 

 Probably not to any great extent ; it is more likely that it 

 secures the decomposition of other substances without being 

 itself materially used up. Such a course would be much 



