Transcript No Slide Title

The Plant Body
Early Stem Growth – the Plumule
Plant Growth – Apical Dominance
Stem Function
• Conduction involves moving substances
manufactured in the leaves through the phloem to
other parts of the plant including developing
leaves, stems, roots, developing flowers, seeds and
fruits
• The xylem carries water from the roots to the
leaves, where water is transpired
• Support involves holding the plant off the ground
• Stems may function to a certain extent in storage
as well, storing material in parenchyma cells
Primary Growth of the Stem
• The apical meristem adds cells to the plant body and forms
leaf primordia and bud primordia that develop into lateral
branches
• The apical meristem of a stem lacks a protective cover like
the root cap of roots
• Protoderm always originates from the outermost meristem
cell layer
• Procambium and part of the ground meristem (which will
form the cortex and sometimes part of the pith) form from
the peripheral meristem
• The rest of the ground meristem (which forms some or all
of the pith) is formed by the pith meristem
Stem Growth
Position of
shoot meristems –
shown by black dot
Increase in primary thickness
• Growth in thickness of the primary body of
the stem involves longitudinal division and
cell enlargement in both cortex and pith - in
plants with secondary growth, primary
thickening of the stem is moderate
• Monocots usually lack secondary growth,
but may have massive primary thickening
and growth (palms)
Monocot primary growth
Primary and
Secondary Stem Growth
Primary Stem Structure
• In some conifers and dicots, the narrow, elongated
procambial cells (and consequently the primary
vascular tissues that develop from them) appear as
a more or less continuous hollow cylinder within
the ground tissue - the outer region of the ground
tissue is called the cortex and the inner region is
the pith
• A good example of this structure is basswood Tilia – it has secondary growth
Basswood or Linden (Tilia)
Primary Stem Structure
• In other conifers and dicots, the primary vascular
tissues develop as a cylinder of discrete strands
separated from one another by ground tissue
• The ground tissue separating the procambial
strands (and later mature vascular bundles) is
continuous with cortex and pith and is called the
interfascicular parenchyma (between the bundles)
• The interfascicular regions are often called pith
rays
Sunflower Stem Structure
Primary Stem Structure
• In most monocots and some herbaceous
dicots, the arrangement of procambial
strands and vascular bundles is more
complex - vascular tissues do not appear as
a single ring, but instead develop as more
than one ring or are scattered throughout the
ground tissue - here ground tissue cannot be
distinguished as pith and cortex – seen in
corn
Corn (Zea mays) stem structure
Relationship of vascular tissue in
leaves and stem
• The pattern formed by the vascular bundles in the
stem reflects the close structural and
developmental relationship between the stem and
its leaves
• at each node, one or more vascular bundles
diverge from the cylinder of strands in the stem,
cross the cortex and enter the leaf or leaves
attached at that node
• The extensions from the vascular system in the
stem toward the leaves are called the leaf traces
Relationship of vascular tissue in
stems and vascular bundles
Leaf Traces and Stem Bundles
• If stem bundles are followed either upward or
downward in the stem, they will be found to be
associated with several leaf traces - a stem bundle
and its associated leaf traces are called a
sympodium
• In stems of some species, some or all or the
sympodia are interconnected
• In other species, all the sympodia are independent
units of the vascular system
Vascular bundles are frequently
arranged in spiral fashion
Leaf Structure
Leaf Internal Structure
• variations in internal structure of leaves are largely due to
growth habit of the plant
• mesophytes are plants that require abundant soil moisture
and a fairly humid environment - the most common plants
- typically have fairly well developed epidermis, especially
on upper surface of leaf, stomata on both sides of leaf
• hydrophyte - plants that depend on a very abundant supply
of water or which grow wholly or partially submerged in
water - have thin epidermis, stomata only on upper surface
• xerophyte - plants adapted to arid habitats - very thick
epidermis, stomata open to stomatal crypts with protective
hairs
Mesophyte Leaf
Hydrophyte Leaf
Xerophyte Leaf
Dicot stomata
Leaf Venation
Leaf Venation
Bulliform cells and leaf curling
Sun vs. Shade Leaves in Oaks