290 VEGETABLE PHYSIOLOGY 



retained in potential form, and hence every cell depends 

 for the maintenance of its energy upon a constant supply 

 of complex material, whose subsequent decompositions 

 will replace the amount of energy which has been utilised 

 in the permanent increase of its substance. 



The translocation of constructed materials which we 

 have already considered must be regarded, therefore, not 

 only as furnishing the materials for nutrition and growth, 

 but also as carrying or distributing throughout the plant- 

 body the kinetic energy absorbed as light or heat by the cells 

 to which these forces are originally supplied. The chloro- 

 phyll apparatus is an important piece of mechanism for 

 the accumulation of energy which is subsequently distri- 

 buted and utilised wherever need arises for it. This is 

 true also of all cells which have the power of absorbing 

 kinetic energy in any form. 



The absorption and fixation of energy involved in the 

 photosynthetic processes carried out by the chlorophyll 

 apparatus can be easily observed, and the immediate fate 

 of such energy can be readily determined. The accumu- 

 lation of the energy of heat is not so easy to trace, but 

 there is no doubt that it proceeds along similar lines. Part 

 of it can travel as kinetic energy, as heat is slowly con- 

 ducted along the tissues of the plant, but ultimately some, 

 at any rate, becomes potential. 



We see, therefore, that wherever any substance that 

 has been manufactured by the plant is stored in a cell, that 

 cell is thereby put in possession of a certain amount of 

 potential energy corresponding to the quantity of such 

 stored material. Even the living substance itself may be 

 looked upon as a further store of energy, as it can liberate 

 it by its own decomposition. 



Each cell is thus supplied through the general activities 

 of the whole plant, not only with the food it needs for its 

 nutrition, but also with the energy required for carrying out 

 its vital processes. The ultimate utilisation of the stored 

 energy is consequently a process which must be studied 



