210 LECTURE XL 



Glucose. Butyric acid. 



C 6 H 12 O 6 =. C 4 H 8 



Malic acid. Lactic acid. Butyric acid. 



2 C 4 H 6 O 5 = 2 C 3 H 6 O 3 + 2 CO 2 = C 4 H 8 O 2 + 4 CO 2 + 2 H 2 . 



De Luca observed, in his experiments, that some acetic acid, which is 

 homologous with butyric acid, was formed in the fruits, flowers and 

 leaves. 



The decomposition of mannite mentioned above may be represented 

 by the following equations ; it may undergo either 



i, alcoholic fermentation, according to the equation, 



C 6 H 14 O 6 = 2 C 2 H 6 O + 2 CO 2 + H 2 , 

 or 2, lactic fermentation, according to the equation, 



butyric and acetic acid are the products of the decomposition of the 

 lactic acid or of the oxidation of the alcohol. 



Further, the absence of free oxygen not only modifies the 

 destructive metabolism of the plant as regards the exhalation 

 of carbon dioxide and of watery vapour, but it apparently 

 modifies it also as regards the nitrogenous products of the 

 'decomposition of proteid. Boehm found, in the experiments 

 mentioned above, that the water in which the plants were kept 

 gradually acquired an alkaline reaction, and that this was due 

 to the presence of ammonia. The conflicting statements as 

 to the evolution of ammonia by germinating seeds, some ob- 

 servers (Hosaeus, Oudemans and Rauwenhoff, Schulz) asserting 

 it, others (especially Detmer) denying it, are probably to be 

 harmonised by the consideration that although it does not 

 take place when free oxygen is present, yet it may do so 

 when the supply of free oxygen is insufficient. Under normal 

 conditions the products of nitrogenous metabolism are princi- 

 pally oxidised substances which are retained by the plant, 

 and if any ammonia is formed it is chemically altered on its 

 formation so that it is not exhaled by the plant: under the 

 abnormal conditions which we are now considering it is ap- 

 parently formed in such quantity that some of it is exhaled. 



From the facts before us we gather that the absence of oxy- 

 gen profoundly modifies the metabolism of plants. The vast 

 majority of plants are so constituted that they can only thrive 



