Botany 1404: Stems
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Botany 1404: Stems
Basics of stems
composed of stem and leaves
has axillary and terminal buds
Functions of the Stem
conduction of water, minerals, and food
: terminal and axillary
: 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)
: 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
: single layer of cells, cuticle over it
no pith/cortex regions, just ground tissue
vascular bundle (xylem, phloem, bundle sheath, airspace)
: go through their entire life cycle in one year, limited secondary growth, generally herbaceous
: two seasons needed to complete entire life cycle, limited secondary growth, generally herbaceous
: 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
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.
: lateral meristem that produces cork and phelloderm.
: heavily suberized walls, non-living.
: 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
conducts water and ions
stems resembling leaves
: prickly pear
stems growing along surface of ground