THE ENEEGY OF THE PLANT 295 



been applied to the construction of the material so burned. 

 Any accumulation of material in the body of the plant 

 represents therefore not only a gain of weight or substance, 

 but a storage of energy. This has disappeared from 

 observation during the constructive processes, but can be 

 liberated again during their decomposition and applied to 

 other purposes. Energy which has thus been accumulated 

 and stored is known as potential energy, to distinguish it 

 from the actual or kinetic energy originally absorbed. The 

 formation of material in the plant therefore involves a 

 storage of energy in the potential form, and wherever such 

 material is found there is an accumulation also of energy 

 which can be liberated with a view to utilisation at any 

 point to which the material has been transferred. The 

 translocation of material therefore involves also a distribu- 

 tion of the energy which, originally absorbed as the kinetic 

 energy of light or heat, has been applied to constructive 

 processes, and has consequently been made potential. 



From these considerations we may see that plants which 

 absorb elaborated food from their environment have a 

 source of energy therein. This food is a store of potential 

 energy which is absorbed as such, and rendered kinetic 

 subsequently. 



It is this potential energy on which the plant depends 

 for the various processes which go on in such cells as are 

 not the recipients of external kinetic energy. Even in 

 the cells which absorb the latter a certain amount of 

 potential energy also is present, which represents what 

 has been stored by them in the constructive processes they 

 carry out, or has reached them in the shape of complex 

 materials formed originally in other cells. 



It is mainly on this store of energy that not only the 

 whole organism but every cell depends for the execution of 

 its vital processes. Each cell is practically the seat of the 

 liberation of this potential energy, or its conversion into the 

 kinetic form, during the decompositions which take place 

 within it. 



