52 NATURE’S FOOD SUPPLY. THE CARBON CYCLE 
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 of decomposition, wood is converted into simple chem- 
ical compounds which join nature’s food-supply in the air. 
By the means thus’indicated the large part of the carbon ex- 
tracted from the air by plants is restored again to the air in the 
form in which it first existed. This carbon cycle is represented 
graphically in the accompanying diagram (Fig. 13). 
* 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 preserved. The 
ordinary decay of timber is brought about by the kind of fungi and bacteria above 
mentioned. Since none of these organisms 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 preserving timber is by thorough drying. 
