128 PLANT RESPIRATION 



applied the term chromogen to various substances which by 

 autoxidation spHt off hydrogen and change to the corresponding 

 pigment. For example, hydroquinone is oxidised to red quin- 

 one by peroxidase, indigo white to blue indigo. All such 

 oxidations are due to a splitting off of two atoms of hydrogen 

 with the formation of water: 



RH. + O = R + HoO. 



According to Palladin, reserve respiratory chromogens are 

 stored in the form of prochromogens. Under this term Palladin 

 included many tannins, glucosides and similar compounds which 

 liberate oxidisable chromogens after hydrolysis. 



The respiratory pigments R which are formed from chromo- 

 gens by oxidation are effective as hydrogen acceptors according 

 to Palladin, while the oxidation of carbon is said by Wieland 

 to take place by means of the oxygen of water. In living tissues 

 the respiratory process, according to Palladin, is initiated by 

 the catalytic dissociation of water. The oxygen of the water 

 oxidises the carbon of the intermediate products of fermentation. 

 The hydrogen of the water and of the respiratory material is 

 thereby temporarily bound to respiratory pigments, i.e. oxidised 

 chromogens. The first phase of respiration may be expressed 

 by the following equation (since the chemical nature of the 

 intermediate products of fermentation is unknown, the respira- 

 tory material is represented here by the empirical formula for 

 sugar) : 



CeHioOe + 6H.>0 -f 12R = 6CO2 + 12RH2. 



From this it is evident that all the CO2 of oxygen respiration 

 is of anaerobic origin, in Palladin's opinion. The carbon of the 

 respiratory material is oxidised by the oxygen of water and of 

 the respiratory material. The second phase of the oxidation 

 processes of respiration consists in the oxidation of the respira- 

 tory chromogens by peroxidase at the expense of atmospheric 

 oxygen (naturally through the intermediate stage of peroxide 

 formation) , whereby all the hydrogen taken from the respiratory 

 material goes into water: 



12RH2 + 6O2 = 12H2O -f 12R. 



