426 The Physiology of Plants BOOK in 



of atoms, which are formed by rearrangement, are split 

 off, while the residue is again built up into a complete 

 biogen molecule at the expense of the materials found in 

 its vicinity, just as in the manufacture of concentrated 

 sulphuric acid the nitrous acid formed from nitric acid by 

 the withdrawal of oxygen is rebuilt into nitric acid with 

 the aid of the oxygen of the air. The substances still 

 present in the living substance in addition to the biogens 

 are merely " satellites " of the biogen molecule, and either 

 serve for its construction or are derived from its trans- 

 formations '. 



This view of respiration presents it then, not as a process 

 of combustion, simple or ' physiological ', but as the expres- 

 sion of the dissimilation going on in the living substance 

 of the organism. 



At the end of the century the discovery of the oxidases 

 directed speculation towards the possibility of their being 

 concerned in the respiratory processes. These researches, 

 however, had not up to that time led to the formation of 

 a different hypothesis, and a consideration of them does not 

 therefore come within our present province. 



We have seen from the experiments of Wortmann and 

 others that respiration continues for a time when the supply 

 of oxygen to a plant is very greatly reduced or even entirely 

 suspended. At any rate, the production of carbon dioxide 

 goes on. Though the observation was made as early as 

 1880, no explanation was for the moment offered. 



These observations bring us to the consideration of what 

 has been for many years known as intramolecular respira- 

 tion, a process which has been considered as supplementary 

 to the true respiratory process and to have the same object, 

 the supply of internal energy to the plant. It is a con- 

 dition which is associated with the absence of a supply of 

 oxygen, and is hence preferably to be called anaerobic. 



It was in 1861 that the first observations bearing upon 

 it were made. Pasteur in that year ascertained that yeast 

 and several species of Bacterium are able to live in the 



