HOW LIFE CAME TO EARTH 177 



The whole living world depends upon the 

 building up of the energy of the sunlight 

 into the chemical energy of these organic 

 colloids which constitute living structures. 

 The energy-transformer is the green cell of 

 the plant, and, directly or indirectly, the 

 energy of all that lives, in the present stage 

 of evolution, arises from this one source 

 transmuted by this one transformer. In the 

 vegetable world itself, those parts of the 

 plant which are not green possess no power 

 of building up energy from inorganic sources. 

 Such parts of the plant obtain organic sub- 

 stances as a source of energy from the green 

 parts, and the colloids of such parts transform 

 these organic compounds into others, use up 

 their energy to supply power for their own 

 processes, grow in size by transmuting the 

 supply into more colloid, or form reserve 

 depots intended primarily for their own use, 

 or that of their next generation, in the shape 

 of seeds, fruits, roots and tubers. The 

 bodies of the plants, including their reserves, 

 are eaten by animals, and are broken up by 

 the digestive juices into soluble compounds 

 which can again be built up into colloids by 

 the already existing colloids of the living cells 

 of the animal. Part of the animal's food thus 

 provided is oxidized and decomposed back 



