FERNS, FOSSILS AND FUEL 
dioxide and water by the plant itself, are assimilated by 
one’s digestive organs. The carbohydrates are partly 
used to build new tissues in the body and partly burned 
to supply the energy necessary to life. In the same way, 
when coal is burned to develop steam for industrial pur¬ 
poses or merely heat for cooking, there is used some of 
the energy that had been stored up by plants hundreds 
of millions of years ago in the form of carbon compounds, 
and fixed carbon made from carbon dioxide and water. 
If some of this energy is now released as heat and light, 
the carbon dioxide and water vapor at last return to the 
atmosphere, from which they originally came. This is 
the life-cycle which has been in operation on the earth 
for untold millennia. 
It is clear, therefore, that no organic life is possible 
without the synthetic process carried on by the chloro¬ 
phyll in plants. Green plants everywhere are the basis 
of other forms of organic life. Animals of all kinds 
are ultimately dependent on them; either they eat the 
organic substances which are produced by green plants, 
or they eat other animals which in turn have lived on 
plants. 
The fungi, which do not contain chlorophyll, are 
necessarily parasitic on other plants or on animals. They 
are a class of parasites which thrive on living organisms 
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