212 LIGHT, VEGETATION AND CHLOROPHYLL 



of subsistence. Before chlorophyll, Hfe may have appeared on 

 the earth, but it would have been dependent on too many 

 fortuitous circumstances to become firmly estabUshed. With 

 the arrival of chlorophyll, it attained its majority; it became 

 independent and could spring into action. 



The Importance of Energy from Chlorophyll 



When we consider the different types of energy which are, 

 or will be, available to us, they all centre round the atom. 



The most common and the best known is chemical energy 

 typified by that accumulated by chlorophyll in starch or 

 wood. These molecules, of which carbon forms the woof, can 

 be broken down or oxidized. All their potential of oxidation- 

 reduction is realized, either in a single operation by burning 

 or by their use as fuel in internal combustion engines, or else 

 by a graduated series of intermediate reactions, as in our 

 own organism. 



The atom properly speaking represents two types of 

 energy, one relating to the nucleus and the other to the 

 electrons. 



Some of the electrons which revolve round the nucleus 

 may be separated from a group of atoms, thus giving rise to 

 a centre of attraction of electrons and an electric current 

 which, at enormous speed, tends to fill the void which has 

 been created. By means of conducting wires, the potential 

 acquired at any place can be very rapidly transported a long 

 distance; electricity enables energy from the Rhone to be 

 used in Paris, but it must be used immediately. In a certain 

 sense, electrical energy has no more existence than the energy 

 of a belt which transmits the motive power from one pulley 

 to another. It is much spoken of because, in our indistrialized 

 world, most of the transport of energy is eff'ected by it and 

 because, for example, a waterfall as well as a stock of coal 

 can be measured by the number of kilowatt-hours that it is 

 capable of supplying ; electrical energy is an accepted standard 

 of energy. 



Although electrical energy is only transitory, because the 



