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The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three classes based on the nature of the cell walls. Parenchyma cells have thin primary walls and usually remain alive after they become mature. Parenchyma forms the "filler" tissue in the soft parts of plants. Collenchyma cells have thin primary walls with some areas of secondary thickening. Collenchyma provides extra structural support, particularly in regions of new growth. Sclerenchyma cells have thick lignified secondary walls and often die when mature. Sclerenchyma provides the main structural support to a plant. == Parenchyma == Parenchyma (, ''para'' meaning "beside", ''chyma'' meaning "in filling") is a versatile ground tissue that generally constitutes the "filler" tissue in soft parts of plants. It forms, among other things, the cortex and pith of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits, and the endosperm of seeds. Parenchyma cells are living cells and may remain meristematic at maturity—meaning that they are capable of cell division if stimulated. They have thin but flexible cellulose cell walls, and are generally polyhedral when close-packed, but can be roughly spherical when isolated from their neighbours. They have large central vacuoles, which allow the cells to store and regulate ions, waste products, and water. Tissue specialised for food storage is commonly formed of parenchyma cells. Parenchyma cells have a variety of functions: * In leaves, they form the mesophyll and are responsible for photosynthesis and the exchange of gases,〔(Leaves )〕 parenchyma cells in the mesophyll of leaves are specialised parenchyma cells called chlorenchyma cells (parenchyma cells with chloroplasts). * Storage of starch, protein, fats, oils and water in roots, tubers (e.g. potatoes), seed endosperm (e.g. cereals) and cotyledons (e.g. pulses and peanuts) * Secretion (e.g. the parenchyma cells lining the inside of resin ducts) * Wound repair and the potential for renewed meristematic activity * Other specialised functions such as aeration (aerenchyma) and support The shape of parenchyma cells varies with their function. In the spongy mesophyll of a leaf, parenchyma cells range from near-spherical and loosely arranged with large intercellular spaces,〔 to branched or stellate, mutually interconnected with their neighbours at the ends of their arms to form a three-dimensional network, like in the red kidney bean ''Phaseolus vulgaris'' and other mesophytes.〔Jeffree CE, Read N, Smith JAC and Dale JE (1987). Water droplets and ice deposits in leaf intercellular spaces: redistribution of water during cryofixation for scanning electron microscopy. Planta 172, 20-37〕 These cells, along with the epidermal guard cells of the stoma, form a system of air spaces and chambers that regulate the exchange of gases. In some works the cells of the leaf epidermis are regarded as specialised parenchymal cells,〔Hill, J. Ben; Overholts, Lee O; Popp, Henry W. Grove Jr., Alvin R. Botany. A textbook for colleges. Publisher: MacGraw-Hill 1960〕 but the modern preference has long been to classify the epidermis as plant dermal tissue, and parenchyma as ground tissue.〔Evert, Ray F; Eichhorn, Susan E. Esau's Plant Anatomy: Meristems, Cells, and Tissues of the Plant Body: Their Structure, Function, and Development. Publisher: Wiley-Liss 2006. ISBN 978-0-471-73843-5〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ground tissue」の詳細全文を読む スポンサード リンク
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