8/27/2014
‘Stem’ Terminology
Stems
• Central Axis of Shoot Portion of Plant
• Mainly Above Ground, But May Be Underground
• Functions
– Supports & Arranges Leaves to Intercept Light
– Support Flowers & Fruits, Hold at Location For Pollination
• Transport Water & Nutrients
• Storage of Plant Food
– Age Can Affect Quality of Stem Carbs For Feed
• Plant Propagation
• Photosynthesis for Succulents
• Shank—Stem That Holds Corn Ear
• Shoot
– Stem + Leaves & Other Structures
• Culm
– Hollow Stem of Grass
• Stalk
– Solid Stem of Grass
• Stem
– Term Used With Broadleaf Crops
• Woody vs. Herbaceous
Stem Morphology
• Broadleaf Plant
– Nodes
• Buds & Branches
– Terminal Bud
– Internodes
– Petioles
Stem Anatomy
• Vascular Bundles of Xylem & Phloem For Water & Carbohydrate
Transport
• Xylem
– Loses Cytoplasm at Maturity so Is Non-Living Tissue
– Tracheids – Overlap
– Vessel Elements – Connect End to End
• Phloem
• Grass Plant
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– All the Above Except Sheaths Instead of Petioles
– Axillary Branches Called Tillers
No Vacuole or Nuclei
Living Tissue
Companion Cells
Sieve Tube Elements – Connect End to End With a Sieve Plate Between
Monocot Main Stem
Monocot vs. Dicot Stem
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Epidermis
Parenchyma Inside
Scattered Vascular Bundles
No Cambium
Vascular Bundles Surrounded by Sclerenchyma or Other
Thick-Walled Cells
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Factors Affecting Stem Growth
Dicot Stem
• Epidermis
• Cortex in Woody Dicots Is Between Epidermis & Ring
of Vascular Bundles
• Vascular Bundles in Circle
– Circle Will Grow Together With Age in Woody Stem
– Vascular Cambium
• Pith in Center of Stem For Food Storage
• Light Intensity
– Lower Light Intensity Promotes Etiolation
= Longer Internodes
• Less Lignin (Strong Fiber in Cell Walls)
• Cloudy Weather, Weed/Crop Shading
• Soil Water
– Affects Internode Length
• Fertility
– Excess Nitrogen Can Promote Excess Stem Elongation, Weaker
Stems & Lodging
• Lodging
– Affects Leaf Orientation
– Reduces Light Interception For Photosynthesis
– Crops Difficult to Mechanically Harvest
• Causes of Stem Lodging
– Shading, Excess Nitrogen, & Excessive Soil Water
– Diseases
– Insect Damage
Specialized or Modified Stems
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Bulbs
Tubers
Corms
Tuberous Roots
Crowns
Tillers
Stolons
Rhizomes
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