254 LIFE OF A TREE. 
should increase, the store laid up by Divine Pro- 
vidence for the use of man will certainly last for 
five hundred years longer! Such a store corre- 
sponds to about 12,025,000,000 tons of carbon.* 
Amazing thought—all this derived from the air! 
The nature of the chemical changes by which 
wood becomes coal would be far too intricate for 
us to study in this little work. We must there- 
fore remain for the present satisfied with the 
bare statement of this apparently unquestionable 
truth, that under appropriate circumstances a se- 
ries of decompositions take place in woody fibre, 
which end in the production of coal. 
The remaining process of decay is the most 
common of all. By means of it, all existing 
forms of vegetation, when they die, are reduced 
to dust, or more properly, to mould. All parts 
of a tree become by this process equally resolved 
into the same substance. It only wants time 
for the solid stem to take the same condi- 
tion and character, in every respect, as the deli- 
cately tissued leaf, or the tender blade of grass. 
The chemical forces attack each alike, the 
only difference being, that the soft and juicy 
* Dr. Schleiden. 
