100 PLANT PHYSIOLOGY 



we first obtain 7-fructose, which later transforms into its inactive 

 modification. It is very probable that this capacity of liberating 

 the most active of all hexoses explains the presence and signifi- 

 cance of sucrose in plant and animal organisms. 



All these investigations show that both alcoholic fermentation 

 and anaerobic respiration, which are closely allied in their 

 chemism and according to the opinion of some authors are 

 identical, represent a complicated catalytic process brought 

 about not only by one, but by several enzymes. Some of them, 

 e.g., glycerophosphatase, belong to the group of hydrolases, 

 i.e., enzymes catalyzing hydrolysis, and the reverse synthesis. 

 Others, e.g., the glycolytic enzyme, which causes the dis- 

 integration of monoses into shorter chains, pyruvic acid or 

 glyceric aldehyde, as well as carboxylase, which splits CO 2 from 

 pyruvic acid, belong to the group of desmolases, for they cause 

 a disintegration of the carbon chain. At present, the term 

 "zymase" is used for designating this whole group of enzymes, 

 the activity of which ultimately results in the disintegration of 

 sugars into alcohol and carbon dioxide. In living cells, all these 

 enzymes work in strict coordination, and fermentation proceeds 

 as smoothly as if it were a simple reaction. But in a killed cell 

 or in the expressed sap, the system is disturbed, and fermentation 

 soon ceases. Hence the total quantity of sugar fermented by 

 various preparations of zymase is always insignificant if com- 

 pared with the amount fermented by Hving yeast cells. How 

 exactly this coordinating action of the living protoplasm is 

 realized i^ not known. 



24. Relation between Fermentation and Respiration. 

 Theories of Respiration of Palladin and Warburg. — It has already 

 been pointed out that higher organisms, when transferred into 

 an oxygen-free air, display anaerobic respiration, which in its 

 main features is essentially the same as alcoholic fermentation 

 caused by yeast. Therefore, the view has been established that 

 alcohoHc fermentation and respiration are closely related phe- 

 nomena, the former being but a preparatory stage for the latter. 



Formerly, the connection between fermentation and respiration 

 was supposed to be of the following nature: The first products 

 formed from sugar are alcohol and carbon dioxide; in an oxygen- 

 free medium the process stops at this point, but in the presence 

 of air, the alcohol obtained is oxidized further to carbon dioxide 



