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
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