Callus

Callus [ Botany ] Plural: calluses or calli	Dictionary of botanic terminology - index of names
Intransitive verb (To callus) callused, callusing, calluses


	In botany a callus is an actively dividing non-organized masses of undifferentiated and differentiated cells tissue that develops on or around an wounded or cut plant surface or that develops during tissue culture of plant parts.

The callus is also the protective tissue, consisting of parenchyma cells, that develops over a cut or damaged plant surface. ( for example in a cicatrix, hardening, indurate, plant process, scar) To callus literarily means "to form or develop hardened tissue."

Callus [ Horticulture - Tissue culture ]

In plant cell biology a callus is a mass of undifferentiated cells (usually cultivated on gel media that develops during tissue culture of plant parts) induced by hormone treatment.

Callus from tissue culture of (Astrophytum caput-medusae)

They are grown in adequate media consisting of water, agar and of a defined mix of macronutrients and micronutrients for the given cell type, much in the same manner as bacteria.
For plant cells, enrichment with Nitrogen, Phosphorus, and Potassium is especially important. A plant cell callus consists of somatic undifferentiated cells (usually thin-walled parenchyma cells) from an adult subject plant.

See also : Callus culture

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Holdfast roots [ Botany ]
Dictionary of botanic terminology - index of names

Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans), develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994