THE ENEEGY OF THE PLANT 299 



its life if new stores are supplied in the shape of further 

 decomposable material which is capable of taking part in 

 the renewed building-up of the living substance. 



Respiration is thus to be looked upon as a process very 

 largely connected with the utilisation of the store of energy 

 which each cell possesses, and to be perhaps primarily 

 concerned in the transformation of that energy from the 

 potential to the kinetic form. The oxygen appears to be 

 necessary mainly for the purpose of exciting those decom- 

 positions of the protoplasm which are so dependent upon 

 its instability. It is not, however, certain that this is the 

 only part it plays. It is possible that some of the products 

 of the protoplasmic disruption are oxidisable substances, 

 and that to a certain extent a direct oxidation of them takes 

 place. There is undoubtedly some evidence pointing in 

 that direction. 



We have, besides the respiratory processes, another series 

 of chemical decompositions going on in plants, in which 

 the self -decomposition of protoplasm is not necessarily 

 involved. We have seen already that many processes of 

 oxidation and reduction are probably always taking place 

 among the substances which are in solution in the wafer 

 with which the cytoplasm is saturated. Besides these, other 

 changes take place in which no oxidation is involved, and 

 this whether oxygen is present or not. If the access of oxygen 

 to a protoplast is interfered with, its normal respiration 

 soon ceases, but very frequently other 'changes supervene, 

 involving decompositions of a different character, which 

 yield, at any rate for a time, the energy required for life. 



Turning from the question of respiration to study other 

 changes which subserve a similar purpose with regard to 

 the local supply of energy, we may first examine such 

 processes as are oxidative. In them all we cannot fail to 

 mark the activity of the protoplasm in carrying them out. 

 The living substance does not however act as a general 

 oxidising agent, but different protoplasts possess specific 

 powers. Certain micro-organisms can cause the oxidation 



