CHEMISTRY OF THE EARTH 99 



The energy-transformer is the green plant- 

 cell aided by the green colouring matter, 

 called chlorophyll, which it contains. The 

 energy which is converted into chemical 

 energy of organic compounds is that of the 

 sunlight, and the simple forms of matter 

 which undergo transformation, are the carbon- 

 dioxide above mentioned, water, and simple 

 inorganic salts containing compounds of 

 nitrogen such as ammonia or nitric acid, and 

 a few common elements of inorganic nature 

 as simple salts taken up from the soil. In this 

 natural laboratory of the plant, energy is 

 introduced into these simple forms, their 

 chemical constitution is thereby changed, 

 and they become storehouses of energy in 

 chemical form. These organic forms of 

 matter, so elaborated, form the food of 

 animals by whose activities they are finally 

 broken down into their original forms, or others 

 closely resembling them, and so the cycle 

 is completed. All energy of all living things 

 is dependent upon green plants, and they 

 in turn are dependent upon the sunlight. 



As will be pointed out later, all commence- 

 ments of life now or earlier must have de- 

 pended on sunlight, but it is highly improbable 

 that the exceedingly complex green cell of 

 the plant formed the starting point. Life 



