A localized thickening and enlargement of the horny layer of the skin. Also called callosity. The hard bony tissue that develops around the ends of a fractured bone during healing. Botany Undifferentiated tissue that develops on or around an injured or cut plant surface or in tissue culture. Botany The hardened, sometimes sharp base of the floret of certain grasses. To form or develop such hardened tissue. See Usage Note at callous.