A twig of the apple, Malus domestica "Blenheim Orange", showing the disease apple canker.The picture shows an advanced canker that has been present on the twig for several seasons. In the centre, the pale cylindrical structure is the wood of the twig. Around this exposed tissue, the bark is raised and appears as a formless cankerous growth. Canker is a common disease of apples, caused by the fungus Neonectria ditissima (syn. Neonectria galligena, Nectria galligena). The fungus infects the tree through wounds (pruning cuts), sites of local damage or scars left by leaf fall. Rarely, an individual canker may not persist, as the bark regrows to cover the site of infection. The twig pictured here is doomed, as the canker slowly girdles it entirely, killing the living tissues under the bark that transport nutrients and water to the growing point (here, above the top edge of the frame)