RESPIRATORY QUOTIENT 103 



amount of carbon dioxide evolved showed a much greater 

 range in variation than did the absorbed oxygen in the same 

 plant in different conditions, the figures obtained in a series 

 of experiments showing a variation of — 14 to 120 per cent, 

 of the average for carbon dioxide, whilst the oxygen varied 

 from o to 48 per cent, of the average. Ruby * observed 

 in the olive that the ratio remained practically constant and 

 was but little affected by the age of the plant or of the organ 

 examined ; generally it is rather higher in leaves from fruiting 

 branches, a fact possibly connected with the greater abundance 

 of available food, and in the early season of the year it is less 

 than unity but later rises to unity. 



In the germination of the white mustard, Brassica alba, 

 Stalfelt f observed that an increase in the partial pressure 

 of oxygen from 20 to 50 per cent, led to an increase in oxygen 

 absorption. In normal conditions, he found that the maximum 

 absorption of oxygen occurred on the fourth day of germination 

 when the ratio C0 2 /0 2 was about 0-50. 



When the carbon dioxide evolved is due to the immediate 

 physiological combustion of available substances, it will be 

 apparent that the respiratory quotient will vary according 

 to the nature of this food. 



Thus, in general terms, if carbohydrate is the immediate 

 respirable substance, the respiratory quotient will be in the 

 neighbourhood of unity ; on the other hand, if fat is con- 

 sumed the ratio will be less than unity owing to the fixation 

 of oxygen by unsaturated fatty acids. Thus in germinating 

 flax, which is fat containing, figures varying from 0-3 to 0-64 

 were obtained by Bonnier and Mangin. 



These ratios are applicable only in those instances where 

 the physiological combustion is complete. But the process 

 may stop at an intermediate stage ; thus the following acids, 



CH,OH COOH COOH COOH CH 2 COOH 

 1 " I 



(CHOH) 4 (CHOH) 4 (CHOH), COOH C(OH) . COOH 



COOH COOH COOH CH,COOH 



Gluconic Saccharic Tartaric Oxalic Citric 



* Ruby : " Ann. Sci. Nat. Bot.," 191 7> 2 °» J - 

 f Stalfelt : " Biol. Zentrlbl.," 1926, 46, 1. 



