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 



CEL 



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 1. 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. 



