A much larger variety work only in felled or dead wood, even after it is placed in buildings or manufactured articles.

In any case the process of destruction is the same.
The mycelial threads penetrate the walls of the cells in search of food, which they find either in the cell contents (starches, sugars, etc.), or in the cell wall itself.

The breaking down of the cell walls through the chemical action of so-called "enzymes" secreted by the fungi follows, and the eventual product is a rotten, moist substance crumbling readily under the slightest pressure.

Some species remove the ligneous matter and leave almost pure cellulose, which is white, like cotton; others dissolve the cellulose, leaving a brittle, dark brown mass of ligno-cellulose.

Fungi (such as the bluing fungus) which merely stain wood usually do not affect its mechanical properties unless the attacks are excessive.
It is evident, then, that the action of rot-causing fungi is to decrease the strength of wood, rendering it unsound, brittle, and dangerous to use.