THE METABOLISM OF PLANTS. 213 



be aroused by a timely supply of free oxygen. In the case 

 of anaerobiotic plants, it appears that they can maintain their 

 life so long as there is any substance left for them to de- 

 compose. 



Finally, the accumulation of the products of metabolism 

 exercises an important influence on the activity of the 

 metabolic processes. In the case of carbon dioxide the accu- 

 mulation has to be very great before any evident effect is 

 produced. De Luca observed that when, in the course of 

 his experiments, the pressure of the carbon dioxide in the 

 closed receiver became very considerable, the evolution of 

 this gas ceased, and Melsens found that alcoholic fermentation 

 was only arrested when the pressure of the carbon dioxide 

 amounted to twenty-five atmospheres. In the case of other 

 products the effect becomes more quickly apparent. Thus 

 alcoholic fermentation by Yeast is arrested when the ferment- 

 ing liquid comes to contain about 14 per cent, of alcohol ; by 

 Miicor racemosus, when the alcohol amounts to 2 5 per cent. ; 

 by Mucor stolonifer, when the alcohol amounts to 1*3 per cent. 

 (Brefeld). Similarly the lactic and butyric fermentations, 

 which are effected by certain Bacteria, are gradually arrested 

 as the proportion of acid increases, and they are resumed 

 when the acid is neutralised. 



With this we complete our consideration of the metabolic 

 processes. In the next lecture we will especially study the 

 physiological significance and the chemical nature of the 

 products which are formed in connexion with these pro- 

 cesses. 



BIBLIOGRAPHY. 



Pfliiger; Archiv, X, 1875. 



Sachs; Flora, 1863. 



Schmidt; Ueb. Legumin und Emulsin; Diss. Inaug., Tubingen, 



1871. 



Wurtz and Bouchut; Le Papa'in, Paris, 1879. 

 Zulkowsky; Sitzber. d. k. Akad. in Wien, LXXVil, 1878. 

 Loew; Pfliiger's Archiv, xxvn, 1882. 



