80 EVOLUTION 



being built up of cells and various modifica- 

 tions of cells. And there is a third deep 

 resemblance, that when we trace a beech- 

 tree or a squirrel back to its individual begin- 

 ning we find a fertilized egg-cell, which 

 divides and re-divides, the body of the plant 

 or animal being built up by continued division, 

 arrangement and differentiation of cells. 

 But important as these resemblances between 

 plants and animals are, the divergence is very 

 profound and expresses one of the great 

 cleavages in evolution. 



It came about through the invention of 

 chlorophyll by some Protists a chemical 

 and physiological achievement of the highest 

 magnitude, which made the life of plants 

 possible, and, through them, that of animals 

 and man. In the complex "photo-synthesis" 

 by which plants build up complex carbon- 

 compounds from the raw materials of water, 

 air and earth, chlorophyll plays an indispens- 

 able part. The still widely prevalent ignorance 

 of this fundamental process of the living 

 world is perhaps the greatest example of the 

 slowness with which the discoveries of science 

 become generally recognized. 



Most plants derive the carbon they require 

 from the carbon dioxide of the air, while 

 only a few (green) animals have this power; 



