Definition of "callus" []

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The _spikes_ are solitary, 1 to 1-3/4 inch long exserted far above the small spathiform leaf-sheaths, peduncles are capillary and scaberulous, pedicels and joints are somewhat flattened, and have along both the narrow margins long, white, ascending hairs; callus is short with a ring of short white hairs."
• "The _spikelets_ are oblong, 1/8 to 1/5 inch long, the callus is short, hairy with long brown hairs."
• "The _sessile spikelet_ consists of four glumes and contains a complete flower and the callus is short and bearded with long hairs."