Tree pine ("Pinus" species) the bark exudes sticky resin which deters attackers whereas in rubber trees ("Hevea brasiliensis") it is a milky latex that oozes out. The quinine bark tree ("Cinchona officinalis") contains bitter substances to make the bark unpalatable. Large tree-like plants with lignified trunks in the Pteridophyta, Arecales, Cycadophyta and Poales such as the tree ferns, palms, cycads and bamboos have different structures and outer coverings. Although the bark functions as a protective barrier, it is itself attacked by boring insects such as beetles. These lay their eggs in crevices and the larvae chew their way through the cellulose
Bark bread known from the 1890s, and in Finland "pettuleipä" (literally "pinewood-bark bread") was produced as ersatz bread during the Finnish Civil War of 1918. Finger sized twigs and branches were collected from deciduous trees and shrubs, and the bark split and the inner bark (the phloem and sometimes the vascular cambium) collected while still fresh. The yellow or green inner bark (depending on tree species) was dried over open fire, in an oven or dried in the sun for a few days. A mortar or mill was used to grind the bark to a fine powder to add to the flour.