THE CHEMICAL PROCESSES IN PLANT RESPIRATION 147 



atoms and oxygen. This has been discussed in previous state- 

 ments. For that reason Boysen- Jensen^ is mistaken in saying 

 that the capacity of plants to ferment sugar directly (i.e. 

 without the use of enzymes of fermentation) is demonstrated 

 by such processes as the oxidation of sorbitol to sorbose, glycer- 

 ine to di-hydroxy-acetone, glucose to gluconic acid, etc. On 

 the contrary, all such reactions furnish striking proofs that, in 

 the direct oxidations in the protoplasm of plant cells, there is 

 only an oxidation of hydrogen and never a disruption of carbon 

 chains. 



The estabhshed limitations, previously stated, were first 

 based on the fact that the mixtures of respiratory enzymes 

 taken from various plants^ exhibit very unlike compositions. 

 Kostychev^ proved this soon after the discovery of zymase. 

 He was able to exhibit from molds capable of fermentation, dry 

 preparations which were in all respects similar to killed yeast 

 (zymin and "Hefanol"). Strongly aerobic molds furnished 

 preparations of enzymes which, outside of living cells, effected 

 a metabolism wholly analogous to respiration and which may be 

 traced to a corresponding quantitative ratio between the 

 enzymes of cleavage and of oxidation. Strongly aerobic fungi 

 contain a large quantity of oxidising inductors. By means of 

 these experiments it was first shown that oxygen respiration 

 represents a fermentative process. Preparations of lasting 

 yeast (Dauerhefe), which consist of killed yeast cells, exert no 

 oxidising effect. As long as only such preparations were known 

 it appeared as if the capacity to use molecular oxygen in an 

 oxidation of organic substances which involved a release of 

 CO2 were peculiar to living protoplasm. Accordingly respira- 

 tion appeared to be not a chemical process but a resultant of 

 heterogeneous material transformations carried out in the proto- 

 plasm, so much the more since it had been known in the mean- 

 time that oxidising enzymes could link oxygen to hydrogen 

 but not to the carbon of organic compounds. As soon as it 



1 Boysen-Jensen, P. toe. tit., p. 29. 



2 This characteristic was first demonstrated by Kostytschew, S. Ber. d. bot. Ges. 

 22 : 207. 1904. 



^Kostytschew, S. loc. cit.; Zentralbl. f. Bakt., Parasitenk. u. Infektionskrankh. (II). 

 13:490. 1904; c/. also Maximo w, N. Ber. d. bot. Ges. 22 : 225. 1904. 



