284. VEGETABLE PHYSIOLOGY 
retained in potential form, and hence every cell is depen- 
dent for the maintenance of its energy upon a constant 
supply of complex material, whose subsequent decomposi- 
tions 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 ig 
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 
conducted 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 
