GREAT STEPS IN EVOLUTION 79 



ning we find fl ^fertilized egg-cell, which 

 divides and re-divides, the body of the plant 

 or animal being built up by continued divis- 

 ion, arrangement and differentiation of cells. 

 But important as these resemblances be- 

 tween plants and animals 



very profound and expresses one of the 

 cleavages in evolution. 



It came about through the__invention o 

 chlorophyll bv some Protists a chemical 

 and physiological achievement of the highest 

 magnitude, whifih.jna.ffc 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 indispen- 

 sable part. The still widely prevalent ig- 

 norance 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; 

 all the others depend for their carbon supplies 

 on the sugar, starch, fat, etc., already made^ 

 \by other animals or by plants. As regards 

 nitrogen, most plants take this from nitrates 

 and the like, absorbed along with water by 



