Leaves213S - Leaves - 1 Leaves are best known as the...

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Leaves - 1 Leaves are best known as the photosynthetic organs of plants, and much of the leaf "architecture" reflects this function. Leaves are part of the plant's shoot system, attached to stems at nodes. The regions along the stem between leaves are internodes. Leaves exhibit far more variation in shape (morphology) than do stems and roots. Leaf shape, size, venation pattern, margins, tips and bases are all used in identification of plant species (with appropriate vocabulary). Most leaves, however, have two common features: the blade (or lamina), the flattened portion of the leaf, and the petiole, or leaf stalk, which attaches the leaf to the stem. Leaves that do not have a petiole are sessile, and often sheath the stem at the base of the leaf. Stipules, small leaf-like growths near the base of the petiole, may or may not be present. Buds are located in the axil of a leaf with the stem. Leaf morphology varies in monocots and eudicots, too, with monocots generally having linear leaves that sheath the stem at the base and eudicots having almost any shape, but typically with a petiole. Eudicot Leaf Monocot Leaf Leaves have a vascular connection to the stem through the petiole. Vascular tissue in leaves comprises the veins. In early development, a procambium strand from the shoot meristem branches out into each leaf primordium. This is the leaf trace. Similar strands of procambium branch out into buds, the bud traces. They leave a procambium gap in the stem tissue called the leaf trace gap and bud trace gap. The traces and gaps can often be seen in the shoot meristem. Leaf venation patterns are also an important distinction between monocots and eudicots. Monocots usually have parallel veins; eudicots have netted veins, generally with a significant midvein. Eudicot leaves may have pinnate venation (with veins branching regularly from the midvein) or palmate venation (with major veins radiating from the leaf base). The Ginkgo tree, which is a gymnosperm, has leaves with dichotomous venation. It is unique. Netted veins Parallel veins leaf
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Leaves - 2 Leaf blades may be simple, dissected or compound with leaflets along the petiole (or rachis) along one plane. A compound leaf can be distinguished from a simple leaf by the location of buds. There are no buds in the axils of leaflets. Compound leaves may be pinnately compound or palmately compound. Compound leaves with three leaflets, such as clover, are said to be ternate. The phyllotaxy, or arrangement of leaves on the stem may be helical (sometimes called alternate with one leaf per node), opposite (two leaves per node) or whorled (three or more leaves per node). The number of leaves along a stem before overlapping is called ranking. In some cases, this leads to a very ordered arrangement, such as the ranking of leaves on most plants in the mint family or in many grasses. Alternate
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Leaves213S - Leaves - 1 Leaves are best known as the...

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