tissue

• 1. The cells of meristematic tissue are similar in structure andhave thin cellulose cell walls.2. The meristematic cells may be spherical, oval, polygonal orrectangular in shape.3. The meristematic cells are compactly arranged and do notcontain any intercellular space between them.4. Each meristematic cell contains dense or abundantcytoplasm and a single large nucleus
• Meristematic cells contain few vacuoles or no vacuoles at all.
• Meristematic tissue is a growth tissue found in the growing regions of the plant.
• Apical meristems are situated at the growing tip of stems and roots, i.e., at shoot apex and root apex.
• Apical meristems are also found at apices of the leaves.
• Lateral meristems are found beneath the bark, occurring in thin layers.
• Cambium is the region which is responsible for growth in thickness.
• Intercalary meristems are located at the base of leaves or internode, e.g., stems of grasses and other monocots.
• Meristematic tissue acts as a parent tissue from which other tissues develop.
• These tissues take part in growth by formation of new cells.
• With the help of meristems, plants continue to produce new leaves, branches of stem and root, flowers, fruits and root hairs.
• The place of injury in plants is healed up by the formation of new cells by meristems.
• The plant shoots lodged or bent by wind are made to grow upright by activity of intercalary meristem.
• Apical meristem brings about the elongation of the root and stem, resulting in an increase in the height of the plant, which is called primary growth.
• Lateral meristem causes the organ (stem or root) to increase in diameter and girth, this is called secondary growth.
• Intercalary meristem produces an increase in the length of an organ such as leaves and internodes.
• Cells derived from division of meristematic tissue take up specific role and lose the ability to divide, forming a type of permanent tissue.
• The developmental process by which cells derived from meristematic tissue, take up a permanent shape, size and function is called differentiation.
• Different types of permanent tissues are formed due to differences in their specialization.
• Permanent tissues may be simple or complex.
• Their cells may be living or dead, thin-walled or thick-walled.
• Thickening may be regular or irregular.
• Parenchyma forms the bulk of the plant body and its cells are living and possess the power of division.
• Parenchyma cells are rounded or isodiametric, i.e., equally expanded on all sides.
• Parenchyma cells are metabolically active; their intercellular air spaces allow gaseous exchange.
• Such a type of parenchyma is called aerenchyma.
• Parenchyma tissue is found in the soft parts of the plant such as cortex of roots, ground tissues in stems and mesophyll of leaves.
• Parenchymatous cells are oval, round, polygonal or elongated in shape.
• Collenchyma cells are elongated in shape and often contain a few chloroplasts.
• In collenchyma, intercellular spaces are generally absent.
• Collenchyma (Gr., kolla – glue) tissue also consists of living cells and is characterised by the deposition of extra cellulose at the corners of the cells.
• In hydrophytes (aquatic plants) such as water hyacinth, Hydrilla, large air cavities are present in parenchyma to give buoyancy to the plants.
• In xerophytes (arid plants), e.g., succulents, parenchyma acts as a water storage tissue.
• Collenchyma provides tensile strength with flexibility to those organs in which it is found.
• Inter-cellular spaces are abundant in parenchyma tissue, which is widely distributed in plant bodies such as stem, roots, leaves, flowers and fruits.
• The cells of collenchyma are located below the epidermis (i.e., hypodermis) of dicotyledon stem and petiole (leafstalk) (i.e., in outer region of cortex).
• Parenchyma tissue stores waste products of plants such as tannin, gum, crystals, resins or inorganic waste, etc.
• Transport of materials occurs through cells or cell walls of parenchyma cells.
• Collenchyma is a mechanical tissue in young dicotyledonous stems and provides mechanical support and elasticity.
• When cells of collenchyma contain some chloroplasts, they manufacture sugar and starch.