Phloem

Phloem [ Botany ]

Dictionary of botanic terminology - index of names


	Phloem is the main nutrients (food) conducting tissue of vascular plants.

In woody plants, the phloem is the inner layer of the bark. It consist of sieve elements, parenchyma cells, fibres and sclereids.

Unlike xylem, the cells that make up phloem are living at maturity and can carry materials both up and down the plant body. Phloem is comprised of sieve elements, which are arranged end to end to form passageways, and companion cells, which are closely associated with the sieve elements even though their exact function is unknown. Mature companion cells have both a nucleus and cytoplasm, while the mature sieve elements contain only cytoplasm; for this reason it is thought that the nuclei of companion cells may control the activities of neighboring sieve elements. Phloem is responsible for distributing the products of photosynthesis, such as amino acids and carbohydrates, from the leaves to the rest of the plant.

Compare with xylem.

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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