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. 
elther by the intervention of the living substance itself 
or an enzyme secreted by it. The oxidation of various 
matters ig 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 0° C. they are incapable of 
effecting any decompositions. 
