8 PLANT RESPIRATION 



The ratio of the expelled carbon dioxide to the absorbed 



CO2 



oxygen is called the respiratory quotient and is written ~(^~ • 



CO- 

 The value of -7^— is subject to various fluctuations which can 



not be traced to the antagonistic incidents of the COo-assimila- 

 tion of photosynthesis in green leaves. The equation of aerobic 

 respiration 



C6H12O5 + 60.2 = 6CO2 + 6H2O 



states, of course, on the basis of the law of Avogadro that the 

 volumes of CO2 and O2 in the gas exchange should be equal. 

 This holds in many cases, but various kinds of deviations from 

 this regularity are possible. This can come from the following 

 reasons. 



I. Simultaneously with the oxygen respiration there also 

 takes place an independent absorption of oxygen for other 

 purposes. The extra oxygen is used in the formation of organic 

 carboxylic acids and other compounds rich in oxygen. In all 



COo 

 such cases -p^- is less than i. As a common example of this 

 O2 



type there are those respiratory processes which occur in seed 

 germination^ just as in general in vigorous growth and vege- 

 tative development.- Also the storage of organic acids in 

 ripening fleshy fruits and in succulents effects a depression of 



rCOo 



the value of r\ ■ 

 U2 



II. In other cases, on the contrary, a surplus of CO2 is formed 



by processes which proceed without an absorption of oxygen. 



Very common is the case in which oxygen respiration and 



alcoholic fermentation take place simultaneously. With this 



CO 

 condition -p.-^ is greater than i. In the early stages of ger- 

 O2 



mination of some seeds whose compact seed coat is scarcely 

 permeable to oxygen, alcoholic fermentation stands out as the 

 normal process of germination, so long as the seed coat is not 



' Bonnier, G. tt Mangin. Ann. des. sci. nat. (VI) i8: J64. 1886. 



sPaHadin, W. Ber. d. bot. Ges. 4: 322. 1886; Constamm. Rev. g6n. de bot. Vol. 25 

 as far as p. 539. 1914- 



