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Leaves of most plants include a flat structure called the blade or lamina supported by a network of veins, a petiole and a leaf base; [1] but not all leaves are flat, some are cylindrical. [ citation needed ] Leaves may be simple, with a single leaf blade, or compound, with several leaflets .
A plant that loses all of its leaves only briefly before growing new ones, so that it is leafless for only a short time, e.g. approximately two weeks. bristle A straight, stiff hair (smooth or with minute teeth); the upper part of an awn (when the latter is bent and has a lower, stouter, and usually twisted part, called the column ).
The plain green leaves of A. cylindraceum appear in early spring (late March–early May) followed by the flowers borne on a poker-shaped inflorescence called a spadix, which is partially enclosed in a grass-green spathe or leaf-like hood. The flowers are hidden from sight, clustered at the base of the spadix with a ring of female flowers at ...
180° (or 1 ⁄ 2): two leaves in one circle (alternate leaves) 120° (or 1 ⁄ 3): three leaves in one circle; 144° (or 2 ⁄ 5): five leaves in two gyres; 135° (or 3 ⁄ 8): eight leaves in three gyres. Most divergence angles are related to the sequence of Fibonacci numbers F n. This sequence begins 1, 1, 2, 3, 5, 8, 13; each term is the ...
Leaves may also be whorled if several leaves arise, or appear to arise, from the same level (at the same node) on a stem. Veronicastrum virginicum has whorls of leaves separated by long internodes. With an opposite leaf arrangement, two leaves arise from the stem at the same level (at the same node), on opposite sides of the stem. An opposite ...
Heliotropism, a form of tropism, is the diurnal or seasonal motion of plant parts (flowers or leaves) in response to the direction of the Sun. The habit of some plants to move in the direction of the Sun, a form of tropism, was already known by the Ancient Greeks.
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The epidermis is the outermost cell layer of the primary plant body. In some older works the cells of the leaf epidermis have been regarded as specialized parenchyma cells, [1] but the established modern preference has long been to classify the epidermis as dermal tissue, [2] whereas parenchyma is classified as ground tissue. [3]