4 PLANT RESPIRATION 



The amount of CO2 given off from a unit of living substance 

 per unit of time serves as a measure of the respiratory energy. 

 Ordinarily one is content with a calculation of the COo-produc- 

 tion per gram of dry weight. Still it is evident that no great 

 accuracy is possible with this kind of calculation. The per- 

 centage of protoplasm is not uniform in the various plants and 

 parts of plants, the respiratory gas exchange of which depends 

 entirely upon the activity of the living substance. Only the 

 cells of embryonic tissues are filled with protoplasm while in the 

 cells of differentiated tissues the plasma at the most forms 

 merely an inner lining of the wall. There are some tissues such 

 as wood and cork, consisting for the most part of dead cells, 

 which do not respire at all. On this account some investigators 

 have attempted to develop more exact methods for the deter- 

 mination of the respiratory energy. 



Palladin^ attempted to explain the dependence of respiration 

 on the amount of living substance through the determination, 

 for the research materials, of the amount of N in the proteins 

 which are undigested by gastric juice. He regarded this nitro- 

 gen as the nitrogen of nuclein which forms the chief part of the 

 protoplasmic structure. The quantity CO2/N, i.e. the amount 

 of CO2 given off from the research material divided by the 

 nitrogen of the undigested protein, is, according to Palladin, the 

 correct measure of respiratory energy, i.e. of the CO2 produced 

 by the unit weight of protoplasm. 



Nevertheless this kind of calculation is also linked with una- 

 voidable sources of error. Gastric juice leaves undigested not 

 only nucleins but also some reserve proteins such as prolamine. 

 But in every case Palladin's method, in spite of objections on 

 the part of various investigators, is more exact than the simple 

 calculation of the carbon dioxide per unit of fresh or dry weight 

 of the research material. 



A still more accurate calculation might be possible, to be sure. 

 For this purpose one should refer the respiratory carbon dioxide 

 to the phosphorus of nuclein or to the purine nitrogen; but such 

 determinations would never be carried out. They are so tech- 



1 Palladin, W. Rev. gen. de bot. 8: 225. 1896; 11: 81. 1899; 13: 18. 1901; Hett- 

 linger.A. /ft/i. 13 : 248. 1901 ; Burlakoflf. Arb. d. Xatiirf.-Ges. in Charkow Vol. 31. 1897; 

 and others. 



