932 LIFE OF A TREE, 
The wood becomes brittle, and crumbles into a 
yellow powder. In damp situations, this change 
takes place very rapidly, producing in the course 
of a few years the most alarming injury to entire 
buildings and ships. It is not clear what the 
exact chemical nature of this change is. It seems 
to be connected with the influence of little fun- 
gous plants which infest timber; but it certainly 
often takes place without fungi being present. 
Another form in which the decay of woody fibre 
takes place is very important for us to consider ; 
it takes place under water. 
Has the reader never plunged his hand beneath 
the waters of the brook in search of ‘ bait,” and 
drawn forth a mass of rotting sticks and chips, 
already turning soft and brown under the in- 
fluence of this form of decay? If he has, he may 
be informed that he has seen the first step in the 
process of the formation of Coal! Were we to 
be asked What is coal? it would probably be 
the best answer to describe it as wood which 
has rotted under water and has afterwards been 
subjected to great pressure from heaps of mud 
overlying it, and which has in consequence of 
these two things, rotting and pressure, become 
ee 
