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Definition of LEAF
a (1): a lateral outgrowth from a plant stem that is typically a flattened expanded variably shaped greenish organ, constitutes a unit of the foliage, and functions primarily in food manufacture by photosynthesis (2): a modified leaf (as a bract or sepal) primarily engaged in functions other than food manufacture
b (1):foliage<trees in full leaf>(2): the leaves of a plant as an article of commerce
: something suggestive of a leaf: as
a: a part of a book or folded sheet containing a page on each side
b (1): a part (as of window shutters, folding doors, or gates) that slides or is hinged (2): the movable parts of a table top
c (1): a thin sheet or plate of any substance :lamina(2): metal (as gold or silver) in sheets usually thinner than foil (3): one of the plates of a leaf spring
Any flattened, green outgrowth from the stem of a vascular plant. Leaves manufacture oxygen and glucose, which nourishes and sustains both plants and animals. Leaves and stem tissue grow from the same apical bud. A typical leaf has a broad, expanded blade (lamina), attached to the stem by a stalklike petiole. The leaf may be simple (a single blade), compound (separate leaflets), or reduced to a spine or scale. The edge (margin) may be smooth or jagged. Veins transport materials to and from the leaf tissues, radiating from the petiole through the blade. They are arranged in a netlike pattern in dicot leaves and are parallel in monocot leaves (seecotyledon). The leaf's outer layer (epidermis) protects the interior (mesophyll), whose soft-walled, unspecialized green cells (parenchyma) produce carbohydrate food by photosynthesis. In autumn the green chlorophyll pigments of deciduous leaves break down, revealing other pigment colors (yellow to red), and the leaves drop off the tree. Leaf scars that form during wound healing after the leaves drop are useful for identifying winter twigs. In conifers, evergreen needles, which are a type of leaf, persist for two or three years.