Plant Growth

• Plants grow throughout their lifetime in two ways:   * Primary growth: Increases length of roots and shoots   * Secondary growth: Increase girth of roots and shoots
• All growth in plants starts at the meristems which function like stems cells in animals and are responsible for producing all tissue of a plant
• Apical meristems: Cause primary growth, are found at the tips of the roots and shoots. Produces primary tissues   * Protoderm: produces epidermis​   * Procambium: produces xylem, phloem and vascular cambium   * Ground meristem: produces cortex, pith, endodermis and cork cambium   * The shoot apical meristem produces the stems, buds, and leaves.   * Monocots have an intercalary meristem that causes leaves to lengthen from their base
• Lateral meristems: Cause secondary growth, are found along the length of the roots and shoots   * Vascular cambium: produces secondary xylem, xylem rays, phloem, phloem rays​. Forms between the primary xylem and phloem. Produces secondary xylem on the inside of the stem and the secondary phloem towards the outside of the stem.     * In herbaceous stems with secondary growth (sunflowers) the vascular cambium produces       * Interfascicular cambium: produces parenchymatous pith rays​       * Fascicular cambium: produces secondary xylem and phloem within the vascular bundles​   * Cork cambium: produces cork, phelloderm​     * Cork cells grow towards the outside and eventually become the outer bark     * Phelloderm grows inwards and becomes the secondary cortex and helps maintain the cork cambium   * Pericycle: located just inside the endoderm and produces lateral roots​   * Xylem and phloem rays are necessary for lateral transport   * Young bark has stomata and as it thickens they become lenticels which continue to allow gas exchange.   * If cork growth keeps up with the increase in girth bark will appear smooth and if it does not keep up the bark will appear cracked.

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