52 THE ORIGIN AND EVOLUTION OF LIFE 



analysis is given here. Potassium is essential for its assimi- 

 lating activity. Iron (often accompanied by manganese), al- 

 though essential to the production of chlorophyll, is not con- 

 tained in it. The chlorophyll-bearing leaves of the plant in 

 the presence of sunlight separate oxygen atoms from the 

 carbon and hydrogen atoms in the molecules of carbon dioxide 

 (COo) and of water (HoO), storing up the energy of the hydro- 

 gen and carbon products in the carbohydrate substances of the 

 plant, an energy which is stored by deoxidation (separation of 

 oxygen), and which can be released only through reoxidation 

 (addition of oxygen). Thus the celluloses, sugars, starches, 

 and other similar substances deposit their kinetic or stored 

 energy in the tissues of the plant and release that energy 

 through the addition of oxygen, the amount of oxygen required 

 being the same as that needed to burn these substances in 

 the air to the same degree; in brief, through a combustion 

 which generates heat.^ Thus living matter utilizes the energy 

 of the sun to draw a continuous stream of electric energy from 

 the chemical elements in the earth, the water, and the atmos- 

 phere. 



This was the first step in the interpretation of life processes 

 in the terms of physics and chemistry, rather than in terms 

 of a peculiar vitalism. What had previously been regarded 

 as a special vital force in the life of plants thus proved to be 

 an adaptation of physicochemical forces. The chemical action 

 of chlorophyll is even now not fully understood, but it is known 

 to absorb most vigorously the solar rays between B and C of 

 the spectrum,' and these rays are most effective in the assim- 

 ilation of energy or food by the plant. While the effect of the 

 solar rays between D and E is minimal, those beyond F are 

 again effective. In heliotropic movements both of plants and 



1 W. J. Gies. -Loeb, Jacques, 1906, p. 115. 



