Radicle

Radicle [ Botany ]

Dictionary of botanic terminology - index of names

The radicle is a part of the plant embryo; It is the first root of the plant that elongates during germination of the seed and forms the primary root.

Usually it emerges from the seed before the embryonic shoot, or plumule, its tip is protected by a root cap, or calyptra, as it pushes through the soil. Roots that branch from the primary root are called secondary roots.
In many plants the primary root is known as a taproot because it is much larger than secondary roots and penetrates deeper into the soil. Beetroots and carrots are examples of plants with very large taproots adapted for food storage.

The radicle may form the basis of the entire root system, or it may be replaced by adventitious roots (positioned on the stem). Grass embryos have a single radicle, but in addition, several other seminal roots form just above radicle; these roots later branch and form a fibrous root system.

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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