Fungi,
live on dead vegetable matter.
Mushrooms grow by means of thread-like feeders which they send down into the dead material which they use.
It is a good thing that fungi use dead trees and leaves and other dead matter for food; otherwise, these things would keep on piling up!
I wish to tell you of one kind of fungus, though, which lives on living material in trees. It is called the—
Bracket Fungus
Perhaps you have thought the bracket-like shelves you have seen on some tree, pretty.
You did not know, then, that some spores of the bracket fungi had fastened into a wound in the bark, and had sent long threads down into the living part of the tree.
The poor tree cannot help itself, and after a while it will die of starvation because the bracket fungi have used up all its food material.
So do be careful never to injure the bark of a tree; for wherever it is torn, it leaves an open wound—just as when you scratch your finger or your arm.