Is a relatively indigestible strengthening polymer that accounts for more than a quarter of the dry mass of wood.

Lignin

It is a complex organic polymer that form an important structural materials in the support system of vascular plants and can also be found in some algae. This is an important molecule in the structural composition of cell wall, such as in wood and bark. This also allow woods and barks to have strong, rigid which allows them to no break easily. Lignin can also be found inserted in the cell wall of this plants.

The answer is a i believe