THE CLASSIFICATION OF FOSSIL PLANTS 
chlorophyll-containing cells, and the sunlight is the energy 
which keeps the process in motion. The fungi, which 
have no chlorophyll of their own, are dependent upon 
the organic substances produced by chlorophyll-contain¬ 
ing plants, as is the entire animal world, including man. 
The opposite of this synthetic process, the building up 
of higher carbon compounds, or carbohydrates, from 
carbon dioxide and water, is the oxidation of organic 
substances back into carbon dioxide and water vapor. 
This is the process carried on through breathing, by 
which the energy needed for plant and animal life is 
produced. The complete chemical cycle is, therefore, the 
building up of organic substances from water and carbon 
dioxide through the energy of sunlight; using a part of 
this substance to form plant and later animal tissue, and 
decomposing the remainder by oxidation to supply the 
energy that keeps the life-cycle in motion. 
This oxidation is a slow process of combustion; it is 
exactly the same in its chemical nature, as the fast and 
intensive combustion which takes place when wood or 
coal is burned, releasing light and heat and producing 
carbon dioxide, water vapor, and ashes. The ashes are 
mineral substance which plant organisms always contain. 
When one eats an apple, for instance, the carbohydrates 
of the fruit, which had been produced from carbon 
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