106 RESPIRATION 



but not so the protein. Carbon dioxide was continually given 

 off, but no intermediate products were detected. In the earlier 

 phases, when the sugar is consumed, and fat and protein syn- 

 thesized, the respiratory quotient is high : but in the later 

 phases, after the sugar has been used up, the amount of car- 

 bon dioxide emitted falls off and the respiratory quotient drops. 

 This change in the respiratory quotient supports the view, 

 based on chemical analyses, that fat is the respirable material 

 of the plant. 



De Boer,* in his investigation of the respiration of Phyc- 

 omyces, found that the respiratory quotient varied accord- 

 ing to the food consumed ; on a linseed substratum, on which 

 the respiration is more intense than on a carbohydrate medium, 

 it ranged from 0-65 to about 075, while on bread, an essentially 

 carbohydrate diet, its average was 1 rising to 1-20 at the peak 

 of respiratory activity. 



With regard to the physiological consumption of proteins 

 in lower organisms, Terroine, Wurmser and Montane f found 

 that Aspergillus niger in conditions of starvation lost relatively 

 much protein ; this fact, taken in conjunction with the ob- 

 servations that on a medium containing glucose the respiratory 

 quotient is in the neighbourhood of unity and falls to 0-8 

 during starvation, % leads the authors to conclude that the 

 plant uses protein rather than carbohydrate as a reserve 

 material. Further, when Aspergillus is grown on a medium 

 containing proteins as the sole source of food, the products 

 of respiration are carbon dioxide, ammonia and water. 



FERMENTATIVE PROCESSES. 

 The equation given on page 102 represents the result of ex- 

 haustive aerobic consumption of carbohydrate. Less economic 

 methods of obtaining energy from carbohydrate are also em- 

 ployed by the plant, the carbohydrate being broken down to 

 products of lower heat energy, but still having considerable 

 potential energy which is possible of exploitation by further 



* De Boer : " Rec. Trav. bot. Neerland.," 1928, 25, 117. 

 f Terroine, Wurmser and Montane : " Bull. Soc. Chim. Biol.," 1922, 

 4. 623. 



X See Kosinski : " Jahrbuch. wiss. Bot.," 1902, 37, 137. 



