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THE STEM. STRUCTURE & FUNCTIONS. General Terminology. Annual – a plant that completes its life cycle (seed, flower, fruit and seed) in one growing season. Ex. Crop plants Biennial – a plant that requires two growing seasons (2 years) to complete its life cycle. Ex. Asparagus
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General Terminology Annual – a plant that finishes its life cycle (seed, blossom, products of the soil) in one developing season. Ex. Crop plants Biennial – a plant that requires two developing seasons (2 years) to finish its life cycle. Ex. Asparagus First year is vegetative development (non-conceptive part) Second years development is regenerative – blossoms and natural products

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General Terminology Perennial – longer lived vegetative plants, keep on living in the wake of blooming and fruiting imitate for a long time (seasons). Illustrations Trees, bushes, numerous blossoming plants: impatiens, periwinkle, dianthus and house plants. Stem – the part of the pivot of vascular plants that is over the ground, and in addition anatomically comparable segments subterranean – rhizomes and corms.

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FUNCTIONS Transport of water & supplements to the top Support Storage Photosynthesis (some of the time)

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Development Primary development From the shot apical meristem primary tissues & expanded stem length, origin of the leaves Secondary development ( for the most part in woody plants; it is restricted in herbaceous plants From the vascular cambium secondary tissues & expanded width From the plug cambium periderm

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Development Apical meristem at the tip From apical meristem you have improvement of the leaf primordia . As the shoot keeps on developing the bud primordia create in the leaf axil. (These will form into different shoots and leaves) As the leaf and bud are framed a strand of xylem and phloem known as the leaf follow , branches off the principle vascular barrel and goes into the stem.

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TISSUE PATTERNS Stele – a focal barrel of vascular tissue (within the cortex) Several unique game plans

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TISSUE PATTERNS Protostele – Most primitive structure, comprising of a strong center of directing tissues, with the phloem encompassing the xylem. Found in a large portion of the wiped out vascular plants and in addition in a hefty portion of the living seedless plants. xylem phloem

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TISSUE PATTERNS Siphonostele – more determined condition, tubular plan with substance in the middle encompassed by the vascular tissue. Found in many plants and numerous gynosperms and angiosprems. Essence Xylem Phloem

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TISSUE PATTERNS Eustele – Primary vascular tissues are organized in various vascular groups around the substance. Vascular packs are strands of tissue involved xylem and phloem and procambium. Vascular Bundle

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Monocot versus Dicot Monocot – Plants that produce one cotyledon, or seed leaf. (Ex. grasses, wheat, palms, grain) Dicot – Plants that produce two cotyledon. Cotyledon – "seed leaf", the main leaf shaped in a seed.

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Monocots Outer layer of epidermis, with a fundamental layer of dead sclerenchyma tissues (filaments) Vascular packs scattered all through the stem, with a higher fixation territory the external border. Which likewise serves to fortify the stem. The rest of the parts of the stem is made out of parenchyma tissues, or ground tissues.

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Cross Section of A Monocot Stem x.s. of Asparagus

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Cross Section of A Monocot Stem X. S. of Zea mays (corn) Vascular Bundle Air Space Center Vessels and tracheids Xylem Phloem Vessels Seive tube components and buddy cells Outside

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Dicots Outer epidermis, with the hidden ground tissues (collenchyma, parenchyma and sclerenchyma) isolated into a cortex and essence. Vascular groups masterminded in a ring underneath the cortex of the stem. With ground tissues between the groups that are persistent between the essence and cortex – interfascicular areas.

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Cross Section of A Dicot Stem Cortex Interfascicular areas Pith

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Stem X.S. of Phaseolus vulgaris

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Activity of the Vascular Cambium Results in Addition of Secondary Tissues

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Secondary Growth of The Stem

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As in roots, the action of the vascular cambium in the stem offers ascend to xylem towards the middle and phloem towards outside. As new cells are included the breadth of the stem increments and the cortex and the epidermis are pulverized and supplanted.

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The Vascular System of A Plant From The Root to The Stem Root

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Secondary Growth of The Stem Formation of auxiliary vascular tissue Secondary xylem & phloem Periderm

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Development Secondary development ( for the most part in woody plants; it is restricted in herbaceous plants From the vascular cambium secondary tissues (xylem and phloem & expanded distance across From the plug cambium periderm

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Growth and Wood sorts Growth rings – development layers which relate to developing seasons. Early wood – "spring wood", wealth of downpour and cooler temperature which permit cells to become bigger and more fast. Late wood – "summer wood", not exactly ideal developing conditions, development moderates. Sapwood – wood found between vascular cambium and heartwood, capacities in the vehicle of water and solutes. Heartwood – wood found in the focal point of the tree trunk, normally darker as a result of pitches, oils and gums. Doesn't transport water or solutes.

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Stem Structures Apical or terminal bud (tip), broadens the length of the stem. Sidelong or axillary buds – build up the shoots or branches and blossoms from the side. Bud scale – terminal bud produces terminal bud scales which shield buds from temperatures, drying up and pathogens. Leaf scars – scar departed on the twig when a leaf tumbles off. Axil – upper point between a twig or leaf and the stem from which it develops. Axillary Bud – Bud that develops from the axil.

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Stem Modifications Rhizomes – flat, subterranean stems, frequently close to the surface with extrinsic roots. (Irises, and grasses) Tuber – plump underground stem, commonly utilized for the capacity of starches. Globule – vast buds with little tapered stems encompassed by huge plump clears out. Corms – Similar to globules, yet contrast in that they are made primarily out of stem materials.

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Stem Modifications