Bark (botany) rope, used for example in the rigging of Viking age longships. Among the commercial products made from bark are cork, cinnamon, quinine (from the bark of Cinchona) and aspirin (from the bark of willow trees). The bark of some trees notably oak ("Quercus robur") is a source of tannic acid, which is used in tanning. Bark chips generated as a by-product of lumber production are often used in bark mulch in western North America. Bark is important to the horticultural industry since in shredded form it is used for plants that do not thrive in ordinary soil, such as epiphytes.
Bark bread bark is the only part of a tree trunk that is actually edible, the remaining bark and wood is made up of cellulose which animals, including humans, cannot digest. The dried and ground inner bark was added in proportions like 1/4th to 1/3rd "bark flour" to the remaining grain flour. Erik Pontoppidan, the Bishop of Bergen, Norway, in the mid 18th century, recommended using elm, as it helped the often crumbly bark bread hold together better. The bark will, however, add a rather bitter taste to the bread, and give particularly white bread an unappetizing grey-green hue. Another problem is