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Published byClaud Franklin Modified over 9 years ago
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STEMS Origin Functions External Anatomy Internal Anatomy
Specialized Stems Physiology 1
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Origin First stem of a plant develops from part of a seed embryo called epicotyl, w/c is a continuation of the hypocotyl
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The Plant Body: Stems FUNCTIONS OF STEMS
Produces & support appendages of plant (leaves, flowers, fruits) transport water and solutes between roots and leaves. Stems in some plants are photosynthetic. Produce & store materials necessary for life (e.g., water, starch, sugar). In some plants, stems have become adapted for specialized functions. 3
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Stems support a display of leaves.
Stems orient the leaves toward the light with minimal overlap among the leaves. 4
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The stem supports a display of flowers
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The stem does photosynthesis… and stores water. Opuntia-prickly pear
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Two Types of Aerial Stems
Herbaceous Stems Woody Stems Soft & green Little growth in diameter Tissues chiefly primary Chiefly annual Covered by epidermis Buds mostly naked Tough & not green Considerable growth in diameter Tissues chiefly secondary Chiefly perennial Covered by corky bark Buds chiefly covered by scales
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Herbaceous Stem woody stem
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EXTERNAL ANATOMY 9
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STEM APICAL MERISTEM 11
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PRIMARY & SECONDARY GROWTH
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Apical Dominance Apical dominance refers to the suppression of growth by hormones produced in the apical meristem. Lateral branch growth are inhibited near the shoot apex, but less so farther from the tip. Apical dominance is disrupted in some plants by removing the shoot tip, causing the plant to become bushy. 16
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INTERNAL STEM ANATOMY 17
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Monocotyledonous & Dicotyledonous Flowering Plants
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Monocot Stem – cross section
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Typical Stem Cross Section (Dicot Stem)
Helianthus annuus- sun flower annual Epidermis Cortex A ring of vascular bundles Pith 20
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- window, reduce water loss
Epidermis - window, reduce water loss Cortex Collenchyma - extensible support Cortex Parenchyma - photosynthesis, etc. Fibers- rigid support Functional Phloem - conduct sugars etc. away from leaf to rest of plant Vascular Cambium - adds 2° xylem and 2° phloem Xylem conduct water and minerals up from soil Pith water storage, defense? 21
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VIP Stem: Provide both name and function labels:
Epidermis: reduce evaporation, gas exchange Cortex: photosynthesis, collenchyma support Vascular Bundles: conduction Pith: water storage? defense? disintegrate? outside to center Vascular Bundle: outside to center Phloem Fibers: support Functional Phloem: conduct CH2O away from leaf Vascular Cambium: add 2° Xylem and 2° Phloem Xylem: conduct minerals up from soil 22
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Vitis vinifera - grape 23
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Remnants of the procambium: Intrafasicular cambium
Notice how the vascular cambia of adjacent vascular bundles line up side by side. Notice that cambium tissue differentiates between the bundles, connecting the cambia together. Remnants of the procambium: Intrafasicular cambium Interfasicular cambium Vitis vinifera - grape 24
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The vascular cambium makes 2° tissues: Vitis vinifera - grape
2° phloem 2° xylem 25
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Basswood – 1 & 2 years old 26
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Three years of Secondary Growth
Tilia - basswood Secondary Phloem cambium Secondary Xylem 27
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A cork cambium differentiates and produces a periderm.
Epidermis cutin suberin Cork Cells Cork Cambium Phelloderm 28
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Over time, the epidermis dies.
The cork cells build up to for a thick layer for the bark of a tree. We use this to make stoppers for wine bottles and so on. When suberin is fully developed, the cortex cells will eventually be in the dark. So these chloroplasts will lose their function! 29
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epidermis + periderm + cortex + phloem + vascular cambium
Bark = epidermis + periderm + cortex + phloem + vascular cambium Wood = secondary xylem only! Pith = a small percentage of tree diameter at maturity 30
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Anatomy of a Woody Stem 31
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The trees pictured below have long lost their epidermis on the woody portion of the stem
Sequoia sempervirens - giant sequoia 32
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The study of the growth rings in wood: Dendrochronology
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Each year the cambium produces a layer of secondary xylem and a layer of secondary phloem.
This photo shows secondary xylem from parts of three years in Pinus strobus (white pine). spring of the next year winter of that year fall of that year mid-summer of one year 34
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Modified & Specialized Stems
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Stolons Stolons or runners - horizontal stem that grow above the ground with long internodes Eg. Bermuda grass (Cynodon dactylon) Spider plant (Chlorophytum) Fern (Nephrolepis) Bermuda grass (Cynodon dactylon). 36
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Rhizomes Rhizomes - horizontal stems that grow below the ground with adventitious roots Eg. irises, ferns, and grasses. 37
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Food Storage Stems Prickly Pear Cactus Bamboo Shoots Kohlrabi 38
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Food Storage Stems - Sugarcane
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Tubers Tubers – swollen regions of stems that store food for subsequent growth The "eyes" of a potato (irish potatoes Solanum tuberosum) are the nodes of a starch-ladened stem 40
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Rosette Rosette - stem with short internodes and leaves attached at nodes 41
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Wild Radish – Rosette & Bolt
A FLOWERING ANNUAL YEAR ONE YEAR ONE 42
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Common Mullen – Rosette & Bolt
A FLOWERING BIENNIAL YEAR ONE YEAR TWO 43
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Bulbs Bulbs - large buds with a small stem at the lower end surrounded by numerous fleshy leaves that store nutrients; adventitious roots at base Eg. onion, tulip, hyacinth, daffodil and lily 44
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Corms Corms - resemble bulbs but composed entirely of stem tissue surrounded by a few papery scale like leaves, food storage organs with adventitious roots at the base of corms Eg. crocus and gladiolus. 45
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Cladophylls Cladophylls or cladodes - leaf-like stems modified for photosynthesis Eg. butcher's broom, asparagus, orchids (eg. Epidendrum) 46
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Succulent Stems Succulent stems - stout fleshy stems that are modified for water and food storage Eg. cacti 47
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Thorns- for protection from grazing animals
Bougainvillea Honey locust (modified stem) Black Locust (modified leaf stipules) 49
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Tendrils – for support Eg. Squash, ampalaya, cadena-de-amor
Grape Tendrils 50
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PHYSIOLOGY OF STEMS Conduction of Materials by Xylem
1) Root pressure – powered by transpiration of water from the leaves 2) Transpiration pull and water cohesion – water is pulled up from the roots due to adhesion of water to the xylem walls & tension generated by the water-potential gradient bet. leaves & xylem Other contributing factors: 3) Atmospheric pressure 4) Action of Living cells 5) Imbibition in cell walls of xylem 6) Capillary attraction
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PHYSIOLOGY OF STEMS Conduction of Materials by Phloem
- nutrient-rich fluid in the phloem moves from areas of high solute concentration & water pressure to areas of low solute concentration & water pressure Hypotheses of phloem function are: 1) cytoplasmic streaming 2) movement through interface 3) pressure flow or mass flow
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Transpiration-Cohesion Hypothesis for Water Movement
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Sugar Loading of Phloem and Bulk Flow
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Sugar Loading of Phloem and Bulk Flow
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