THE TRANSFORMATION OF CARBON. 
45 
gradually they penetrate the hard wood and, by the chemical 
excretions they produce, soften this hard, tough substance. With- 
out the growth of such fungi in the wood there would seem to 
be no way of softening the wood sufficiently for decay. After the 
wood has been somewhat softened by the fungi, wood-eating in- 
insects begin their work upon it, using the fungi largely as food. 
It is probable that bacteria also may assist in this matter, but 
RCH 
TERIA 
VARIOUS CARBON 
COMPOUNDS BUT 
EVENTUALLY ALL 
REDUCED TO C0 2 
IN ATMOSPHERE 
FIG. 13. The carbon cycle. 
the larger fungi are chiefly responsible for the destruction of the 
woody tissue.* The final result is that the carbonaceous material 
in the wood is liberated by being combined with oxygen, and passes 
off into the air to join the atmospheric store of carbon. The 
hydrogen and oxygen are converted into water, and in their turn 
enter the atmosphere as water vapor. In this way, by a slow process 
*These same processes, so useful in the general changes in nature, are 
of decided disadvantage when they occur in timber that is desirable to 
be preserve-i. The ordinary decay of timber is brought about by the 
kind of fungi and bacteria above mentioned. Since none of these or- 
ganisms can grow without water, it follows that well-dried wood will not 
decay, from which is to be drawn the lesson that the best method of pre- 
serving timber is by thorough drying. 
