CALLUS

Cal″lus (kăl″lŭs), n. [[L. See Callous.]] 1. 1. (Med.) (a) Same as Callosity. (b) The material of repair in fractures of bone; a substance exuded at the site of fracture, which is at first soft or cartilaginous in consistence, but is ultimately converted into true bone and unites the fragments into a single piece.
2. 2. (Hort.) The new formation over the end of a cutting, before it puts out rootlets.