black heart
/ˈblak ˌhɑːt/noun
1Any of several cultivated varieties of sweet cherry producing dark-coloured fruit.
2 Agriculture and Horticulture. Any of various plant diseases in which blackening of inner areas of plant tissue takes place; specifically a disease of potatoes characterized by a blackening at the centre of stored and growing tubers, caused by oxygen deprivation such as may result from temperature extremes, waterlogging, or poor ventilation.
3 Metallurgy. A type of malleable cast iron containing nodules of graphite in a ferrite matrix. Contrasted with white heart.
Origin
Mid 17th century; earliest use found in John Evelyn (1620–1706), diarist and writer. From black + heart.