302 VEGETABLE PHYSIOLOGY 
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 has become known as its 
fermentative power. The very similar processes set up 
through the enzymes which we have discussed in connection 
with digestion 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-decompo- 
sition 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 pro- 
bably supplied to them in a similar form, for at 0° C. they 
are incapable of effecting any decompositions. 
We must not suppose that anaerobic respiration is 
capable permanently of taking the place of the normal 
aerobic process. Though the stoppage of oxygen can be to 
a certain extent compensated for, the vital mechanism 
