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- composed of stem and leaves
- has axillary and terminal buds
Functions of the Stem
- conduction of water, minerals, and food
- buds: terminal and axillary
- bud scales
- Nodes: comprised of axillary bud and leaf. Can have multiple leaves attached.
- Internodes are the space between nodes.
- has the shoot apical meristem
- phytomere; has axillary bud, node, internode, and leaf.
- Leaf primordia; develops into leaves
- Axillary primordia; develops into lateral shoots
- trichomes (small extentions of epithelial cells)
- epidermis: single layer of cells, cuticle over it.
- Cortex composed of collenchyma and parenchyma cells
- Vascular bundle (xylem, phloem, vascular cambium)
- Pith composed of parenchyma cells
- epidermis: single layer of cells, cuticle over it
- no pith/cortex regions, just ground tissue
- vascular bundle (xylem, phloem, bundle sheath, airspace)
- annuals: go through their entire life cycle in one year, limited secondary growth, generally herbaceous
- Biennials: two seasons needed to complete entire life cycle, limited secondary growth, generally herbaceous
- Perennials: vegetative structures live year after year, undergo secondary growth, can be herbaceous or woody.
- monocots have no vascular cambium
- vascular cambium produces secondary xylem and phloem.
- When 2 cells go out, 1 differentiates.
- it alternates differntiation between xylem - phloem
- rings on trees are rings of xylem
- outside part of stem
- produces cork cells to outside and cork parenchyma (phelloderm) to the inside
- produces periderm
Secondary Growth in Stems
- within vascular bundle, the fasicular cambium forms from the procambium.
- In pith rays, interfasicular cambium forms between bundles.
- at the end, remnants of cortex, pith, and epidermis.
- peridem forms
- 3 parts
- cork cambium: lateral meristem that produces cork and phelloderm.
- cork: heavily suberized walls, non-living.
- cork parenchyma: phelloderm, living.
region of cork that allows gas exchange between intracellular spaces and the atmosphere.
- all tissues outside of vascular cambium (cork cambium, cork parenchyma, cortex, secondary phloem).
- inner bark (living bark, tissue between vascular and cork cambium)
- phloem that is nonconducting is nonfunctional phloem
- functional phloem is conducting.
- secondary xylem is wood
- has a combination of tracheids, vessel fibers, fibers, and parenchyma cells.
- Occur in temperate regions (regions with seasons)
- periodic activity in vascular cambium produces growth in secondary xylem and phloem (growth rings)
- more water available = bigger xylem cells = thicker ring
- Factors in rings: temp, light, species, soil water availability, rainfall, and length of growing season.
- darker, non-conducting wood
- provides structural support
- dead tissue
- conducts water and ions
- dead tissue
- stems resembling leaves
- ex: prickly pear
stems growing along surface of ground
- w/contractile roots
- ex: bulbs