Acidic

Acid [ Chemistry ]	Dictionary of botanic terminology - index of names


	*Any of various water-soluble compounds having a sour taste and capable of reacting with a base to form a salt.*

A molecule with a positively charged hydrogen that it is capable of donating (A proton donor; i.e. a reducing agent; an electron pair acceptor). Acidity: the strength (concentration of hydrogen [H+] ions) of an acidic substance; measured as pH. Acidify: Make acidic by adding an acid. In most cases when we say acidify we mean lower the pH to pH 7 or less.

Acidic [ Chemistry - Agronomy -Pedology ]

The condition of water or soil that contains an excess of acids, or hydrogen ions (H+) Having a pH less than 7. The opposite of basic.

In general it is defined acidic any substance which contains hydrogen and which dissolves in water to produce one or more hydrogen ions. A lemon is acidic. Acidity is commonly measured using the pH scale.
Acidic soils are those that have a high amount of exchangable hydrogen ions (H+) that can be rendedered free or active in the soil solution by cation exchange. Acidic soils have a low pH (less than 7.0).

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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