308 VEGETABLE PHYSIOLOGY 



extended to include them, and the organisms themselves 

 were called ferments. As, however, these processes have 

 come to be recognised as normal in many of the higher 

 plants, and to be carried out in them by the protoplasm of 

 particular cells, this peculiarity is seen not to be special to 

 the microbes and the fungi. The idea was soon transferred 

 to the protoplasm in general, and this property of setting 

 up anaerobic decomposition became known as its fermenta- 

 tive power. The very similar processes set up through the 

 enzymes which we have discussed in connection with diges- 

 tion show us another manifestation of the same fermentative 

 power. All these processes can therefore be classed under 

 the one term fermentation. We have seen that all the 

 katabolic changes in which the self-decomposition of the 

 protoplasm is not directly involved may be carried out 

 either by the intervention of the living substance itself 

 or an enzyme secreted by it. The oxidation of various 

 matters is in some cases confined to the substance of the 

 protoplasm itself, and is in others carried out in its vacuoles 

 by an oxidase ; alcoholic fermentation is in some cells a 

 matter initiated and carried on by their protoplasm, and in 

 others is due to the enzyme secreted by them. The digestive 

 changes can similarly be conducted by enzymes or by the 

 living substance without their intervention. 



We must not, however, include all digestive fermenta- 

 tive changes among anaerobic respiratory phenomena, if 

 such inclusion involves the acceptance of the view that 

 this is their primary purpose. Though they do effect 

 the conversion of potential into kinetic energy, this is 

 wholly subsidiary to their function in connection with the 

 nutrition of the plant. We have seen that in the processes 

 of germination the energy they liberate is so far in excess 

 of the requirements of the cells that a large amount escapes 

 in the form of heat. For them to work, indeed, there must 

 be an initial supply of energy, which is probably supplied to 

 them in a similar form, for at C. they are incapable of 

 effecting any decompositions. 



