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.