Leaf

Leaf [ Botany ]

Dictionary of botanic terminology - index of names


	A leaf is an outgrowth from a node on a plant's stem and come in many shapes and sizes, they are often green and flattened to maximise their surface area for the capture of energy from sunlight and exchange gases, that are used for photosynthesis by means of the chlorophyll pigment contained in chloroplasts.

Leaves vary greatly from plant to plant and are useful in classification and identification. Some leaves also store food and water, provide support, or form new plants. Where high light intensities are harmful, leaves may reduce the effects of the light by orientating themselves vertically; by becoming thickened or covered with hairs or wax or by having a highly reflective surface.

Leaf Parts: Any of these parts may be lacking, modificate or reduced. Lamina: The expanded portion or blade of a leaf.
Leaf apex: The tip of a leaf opposite to the petiole
Midrib The the central vein of a leaf it is usually continuous with the petiole.
Vein: The vascular structures on a leaf which arrangement is called venation.
Petiole: The stalk or stem that connects the leaf to the plant, frequently with a basal enlargement called pulvinus (petiole are absent in sessile leaves)
Axil: The angle between the upper side of the stem and a leaf or petiole
Stem (also called the axis) from which the leaves arise.
Stipule: The pair of small, appendages one on each side at the base of the petiole.

The forms of leaves lamina vary greatly from plant to plant and are useful in classification and identification.
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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