typesof stemindicots.pdf
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Plant AnatomySEMESTER -06
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Types of Stem In Dicots
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StemDicotyledonous stemExternal Stem StructureTypes of StemHerbaceous Dicot stemWoody Dicot Stem
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Stem❖ Stems are usually above ground organs andgrow towards light (positively phototropic)and away from the ground (negatively
geotropic), except in the case of certain
metamorphic (modified) stems.❖ Ranging from rope like Vines to massive Treetrunks.❖ Either Herbaceous or Woody.
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External Stem Structure❖ Bud – A stem's primary growing point. Buds can beeither leaf buds (vegetative) or flower buds (reproductive). ❖ Terminal bud – Bud on end of a branch, where all ofnext years length (of branch) is added.
❖ Lateral buds grow from the leaf axils on the side ofa stem. ❖ Bud scales – A modified leaf protecting andcovering a bud ❖ Naked bud – Bud without a protective bud
scale;characteristic of the Viburnum family.
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❖ Leaf scar – Mark left on stem where leaf was attached. Often used in woody plant identification.❖ Bundle scar – Marks left in the leaf scar from the vascular tissue attachment. Used in woody plantidentification.
❖ Lenticel – Pores that allow for gas exchange❖ Terminal bud scale scars or annual growth rings – Marks left on stem from the terminal bud scales inprevious years. Terminal bud scale scars are an external measure of annual growth.
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❖ Node-Segment of stem where leaves andlateral buds are attached.
❖ Internode – Section of a stem between twonodes.
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Types of DicotyledonousStems❖ Herbaceous Dicot Stem❖ Woody Dicot Stem
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Herbaceous Dicot Stem❖ Stems with only primary growth
are herbaceous. ❖ e.g Young Sunflower stem
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Internal Structure of Herbaceous Dicot Stem❖ Epiderm❖ The epidermis consists of a single layer of living cells which are closely
packed ❖ Cuticle ❖ Stomata ❖ Cortex❖ This region comprises the collenchyma, parenchyma and endodermis. It issituated to the inside of the epidermis.
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❖ CollenchymaThese cells lie under the epidermis and constitute three to four layers of cells withcell walls thickened at the corners❖ ParenchymaBeneath the collenchyma cells are a few layers of thin-walled cells, parenchyma, withintercellular spaces❖ Vascular BundlesThe vascular bundles are situated in a ring on the inside of the pericycle of the plant.This distinct ring of vascular bundles is a distinguishing characteristic ofdicotyledonous stems
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Epidermal hairs
Hypodспmis r �ਂ Fo Hypoems collen.chyma) తా - بٹیا!Parenchyma} Cortex
" ព្ Middle ألحكـ தி نتيجة HE ÈY–Resinous canal వ్రై� ԱԱrtՅ:X - - శ్రీ� o Vascular bundles
బ్రీ�Bundle caps Vascular
Metaxylem o Xylem fibre – Est Medullary rays ProtoxylernPith
Fig. 3.5.1 : T.S. of young dicot stem Fig. 3.5.2 : T.S. of young dicot stem(Sunflower) ground plan (Sunflower) - A sector enlarged
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❖ Phloem fiber capPhloem contains a cluster of fiber towards the outside of vascular bundles.
❖ Pith (Medulla)The pith occupies the large central part of the stem. It consists of thin-walled parenchyma cells with intercellular air spaces. Between each vascular bundle is a band of parenchyma, the medullary rays, continuous with the cortex and the pith.
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Woody Dicot Stem❖ Plants with primary and
secondary growth ❖ Flowering plant, all have dicot
stem ❖ E.g apple , maple
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Internal Structure of Woody StemPrimary tissues in woody dicots are organised like those in herbaceous dicot stem.❖ Woody dicot stem has three distinct areasBark( cork, cork cambium and phloem)Wood (containing xylem)Pith .
❖ Vascular CambiumProduce secondary xylem and secondary phloem
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As secondary xylem is deposited, the cambium continues to move outward. The cambium, being continuously enlarged, must make not only xylem and phloem, but also additional cambial cells.
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sieve plates❖ The most prominent elements ofphloem are those that compose the sieve tubes. These elements are elongated cells arranged end to end and having perforated end walls.
❖ sieve-tube elements, havingcytoplasm, are living
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Lenticels❖ Bark often possesses
openings ❖ to allow an exchangeof gases
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Spring woodContains wide vessel elements
Summer WoodContains lower portion of wide vessel elements
Numerous fibers and thick walled trachieds.
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Sapwood Heartwood Bark Herw000 andSepw000 -o-,
".o - Periderm
• HeartWOOdlies at the Center of Older ....
No. 7 | Cork cambium stems and roots. o con.
–It depository for resins, oils, gums and tannins o- o | -
– It makes tree Strong and able to defy gravityl | ||
| | .-
O SapW00d. is secondary growth located between heartwood and the Vascular
o o o ു�ണ - o ಗ್ಲಿ�..... m Wet pale in color and is not stong – Rich in the Sugar-
lich fluid of the phloem|
Wascular cambium
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RefrencesBiologyBy Eldra Solomon, Linda Berg, Diana W. MartinCompetition Science Vision Nov 2004A Text Book Of botany: Plant Anatomy and Economic Botany, Volume 3By Pandey S N, S. N. Pandey, Ajanta Chadhhttp://www.biocyclopedia. com/index/introduction_to_botany/the_woody_dicot_stem.phphttp://www.botany.uwc.ac.za/sci_ed/grade10/anatomy/stemhttp://www. biologydiscussion.com/shoot-system/stems/dicotyledonous-stems/dicotyledonous- stems-regions-structure-and-types-botany/20424s.htm#top
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