Stems Outline External Form of a Woody Twig Stem Origin in addition to Development Stem Tis
Sebesta, Jerrid, Meteorologist has reference to this Academic Journal, PHwiki organized this Journal Stems Outline External Form of a Woody Twig Stem Origin in addition to Development Stem Tissue Patterns Herbaceous Dicotyledonous Stems Woody Dicotyledonous Stems Monocotyledonous Stems Specialized Stems Wood in addition to Its Uses External Form of A Woody Twig Woody twig consists of an axis with attached leaves. Alternately or Oppositely arranged. Leaves attached at a node. Stem region between nodes is an internode. Leaf has a flattened blade in addition to is usually attached to the twig by a petiole.
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External Form of A Woody Twig Axil – Angle between a petiole in addition to the stem. Axillary Bud located in axil. Terminal Bud often found at twig tip. Stipules – Paired appendages at the base of a leaf. Often remain throughout leaf life span. Deciduous trees in addition to shrubs have dormant axillary buds with leaf scars left after leaves fall. Bundle scars mark food in addition to water conducting tissue. Origin in addition to Development of Stems Apical meristem is dormant be as long as e the beginning of the growing season. Protected by bud scales in addition to by primordia. When a bud begins to exp in addition to , apical meristem cells undergo mitosis in addition to three primary meristems develop.
Primary Meristems Protoderm – Gives rise to epidermis. Procambium – Produces primary xylem in addition to primary phloem cells. Ground Meristem – Produces tissues composed of parenchyma cells. Pith: center of the stem in addition to consists of parenchyma. Cortex: tissue between epidermis in addition to vascular tissue. Fig. 6.2 As xylem in addition to phloem branch to reach a leaf or a branch, they leave behind a gap in the cylinder of vascular tissues. This gap is called leaf gaps or bud gaps in addition to is filled with parenchyma cells.
Fig. 6.3 Origin in addition to Development of Stems Narrow b in addition to of cells between the primary xylem in addition to primary phloem may become vascular cambium. Cells produced by the vascular cambium become components of secondary xylem in addition to secondary phloem. In many plants, a second cambium, cork cambium, arises. Produces cork cells in addition to phelloderm cells (parenchyma like). Lenticels develop as woody stem ages. Fig. 6.4
Tissue Patterns in Stems Steles Stele is made up of primary xylem, primary phloem, in addition to pith (if present). Protostele – Solid core. Phloem usually surrounds the xylem. In primitive seed plants, whisk ferns in addition to club mosses. Siphonosteles – Tubular with pith in center. Common in ferns. Eusteles Primary phloem in addition to primary phloem are in discrete vascular bundles. Found in most present day flowering plants in addition to coniferns. Tissue Patterns in Stems Dicotyledons – Flowering plants that develop from seeds having two seed leaves (cotyledons). Monocotyledons – Flowering plants that develop from seeds with a single seed leaf (cotyledon). Herbaceous Dicotyledonous Stems In general, annuals (from seed to maturity within one growing season) are green, herbaceous plants. Most monocots are annuals, but many dicots are also annuals. Herbaceous dicots have discrete vascular bundles composed of patches of xylem in addition to phloem. Procambium produces only primary xylem in addition to phloem, but vascular cambium arises later in addition to adds secondary phloem in addition to xylem to the vascular bundles.
Fig. 6.5 A cross section in sunflower (Helianthus) stem showing tissue arrangements of a herbaceous dicot stem
Woody Dicotyledonous Stems Vascular cambium of a typical broadleaf tree produces relatively large vessel elements of secondary xylem (spring wood). Xylem produced next has smaller or fewer elements, in addition to is referred to as summer wood. One years growth of xylem is called an annual ring. Woody Dicotyledonous Stems Vascular cambium produces more secondary xylem than phloem, thus bulk of a tree trunk consists of annual rings of wood. Examining rings can determine the age of a tree, in addition to provide some indications of climatic conditions. Vascular Rays consist of parenchyma cells that function in lateral conductions of nutrients in addition to water. Xylem Ray Phloem Ray
Fig. 6.6a Fig. 6.7a Fig. 6.7b
Woody Dicotyledonous Stems Older, darker wood at the center is called heartwood, while the lighter, still-functioning xylem closest to the cambium is called sapwood. Sap wood is as long as med at roughly the same rate as heartwood. Softwood – Xylem consists primarily of tracheids; no fibers or vessel elements. This occurs in pines in addition to other cone-bearing trees. In woody dicot trees, the xylem contains fibers in addition to vessels elements so it is called hardwood. Woody Dicotyledonous Stems Bark – Refers to all the tissues outside the cambium, including the phloem. Mature bark may consist of alternating layers of crushed phloem in addition to cork. Some scientists can distinguish between inner bark, consisting of primary in addition to secondary phloem, in addition to the outer bark, consisting of cork tissue in addition to cork cambium
Fig. 6.9 Fig. 6.10 Tyloses a. Protoplasts of parenchyma cells protrude into adjacent vessels or tracheids b. Prevent further conduction of water in addition to minerals Resin canals conifers in addition to tropical flowering plants (olibanum trees produce a fragrant resin used in incense [frankincense]; myrrh trees produce a resin called myrrh)
Review External Form of a Woody Twig Stem Origin in addition to Development Stem Tissue Patterns Herbaceous Dicotyledonous Stems Woody Dicotyledonous Stems Monocotyledonous Stems Specialized Stems Wood in addition to Its Uses Copyright © McGraw-Hill Companies Permission Required as long as Reproduction or Display
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