callus(redirected from external callus)
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callus:see corns and callusescorns and calluses,
thickenings of the outer layer of skin where there is irritation or constant pressure. Corns are cone-shaped with their points protruding into the dermis, or inner layer of skin. They usually have hard, shiny surfaces surrounded by red, painful areas.
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(1) Tissue formed in plants on the surface of a wound (cracks, taps, the bases of cuttings, and areas of concrescence of stock and scion). A callus promotes the healing of wounds. Consisting of thin-walled parenchymal cells, a callus develops when there is cell division of any living tissue of the plant (cambium or phloem) in the peripheral zone of the pith, lying next to the protoxylem. Adventitious roots and buds, particularly with grafting, often develop in the callus. (2) Corpus callosum, an accumulation of callóse that obstructs the sieve plate when the sieve tubes of the phloem age. Use of the term in this sense is obsolete.
a thickening of the horny layer of skin as a result of constant pressure or friction. Calluses usually appear on the palms, soles, and other parts of the body that are in constant contact with tough surfaces. The cracks formed on the surface of a callus may hinder one’s ability to work, and they can also be portals of entry for pyogenic microbes, resulting in such conditions as erysipelatous inflammations and phlegmons.