Tannins are common in leaf tissues - particularly in the cells of the upper epidermis (on the top surface of a leaf). It is thought that they reduce the palatability/"tastiness" of the tissue thereby offering protection against herbivores. In the roots, tannins may be present again just below the epidermis offering some protection against the entry of pathogens. The tannins are also found in the the heartwood (sometimes referred to as the duramen), it is the dead, central wood of trees. Tannins make it dark in colour and sometimes aromatic (as in Cedar).

Tannins are common in leaf tissues - particularly in the cells of the upper epidermis (on the top surface of a leaf).   It is thought that they reduce the palatability/"tastiness" of the tissue thereby offering protection against herbivores.   In the roots, tannins may be present again just below the epidermis offering some protection against the entry of pathogens.  The tannins are also found in the the heartwood (sometimes referred to as the duramen), it is the dead, central wood of trees.  Tannins make it dark in colour and sometimes aromatic (as in Cedar).