Lignin is a non-carbohydrate substance, produced in plants. Lignin functions in strengthening plant tissues by binding to the sugar cellulose. Since lignin is not easily acted upon by digestive enaymes, bacteria and insects cannot damage wood as much as would be possible if lignin weren't present. Only a few species of bacteria and fungi can digest lignin. In fact, even the termite relies on bacteria to assist it in digesting the wood it feeds on.