4/5/2013

Stems BI 103: Plant & Animal A & P Outline: 1. Stems: monocots vs dicots--handout 2. Woody plant growth 3. Discussion problems 4. Monocots & Dicots- outside

Plant Anatomy: Vegetative Organs

Leaves: Stem: Photosynthesis Support Gas exchange Transport Light absorption Storage

Roots: Anchorage Storage Form = Function Transport Absorption

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Tissue Patterns in Stems

Cotyledons - Seed leaves attached to embryonic stems Function: Store food needed by young seedling

1. Dicotyledons (Dicots) - Flowering plants that develop from seeds having two cotyledons

2. Monocotyledons (Monocots) - Flowering plants that develop from seeds with a single cotyledon

Plant Anatomy: Monocot vs. Dicot Vascular Number of Leaf Number of Roots bundle pattern Cotyledons Venation Flower Parts in stem Monocot G.

B. D. H. I. Dicot F.

C. J. E. A.

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Organs: STEM

DICOT MONOCOT

Herbaceous Dicot Stems

Have discrete vascular bundles arranged in a cylinder.

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Tissue Patterns in Stems - Monocots Have neither a vascular cambium nor a cork cambium. Produce no secondary vascular tissues or cork Primary xylem and phloem in discrete vascular bundles scattered throughout the stem – Vascular bundles oriented with xylem closer to center of stem and phloem closer to surface. Cross – Parenchyma (ground section of tissue) surrounds monocot vascular bundles. stem

Typical herb vascular bundle

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Specialized Stems: Rhizome

1. Rhizome: underground stem Ferns Potatoes Ginger

Specialized Stems: Runners

2. Runners: Horizontal stems that grow above ground and have long internodes.

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Specialized Stems

3. Stolons – Arching stem produced beneath the surface of the ground.

Dogwood: Cornus serecia

Specialized Stems 4. Corms - Resemble bulbs, but composed almost entirely of stem tissue, with papery leaves Store food Crocus and gladiolus 5. Cladophylls - Flattened, leaf-life stems of cactus

Prickly pear cactus

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Stem Growth 1. Primary Growth A. Apical meristem – increases length B. Ground meristem – makes cortex & pith

2. Secondary growth A. Vascular cambium – produces secondary Xylem & Phloem B.Cork cambium– produces bark to reduce water loss & protects stem (in woody plants only).

Primary vs. Secondary growth

Primary Growth Secondary Growth  All plants  Woody plants only  (only Dicots)  Vertical growth  up or down  Horizontal growth: girth

 Plant gets taller  Plant gets wider

 Where: Meristem tissue  Where: vascular in roots & buds cambium, cork cambium

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Origin and Development of Stems Narrow band of cells between the primary xylem and primary phloem is the vascular cambium. Cells produced by the vascular cambium become the secondary xylem toward center and secondary phloem toward surface.

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Woody plants

Joshua tree (Yucca • Plants brevifoliawith secondary) is growth NOT a woody plant because• Think it doesn’t bark have secondary growth!

External Form of A Woody Twig

Deciduous trees and shrubs (lose all leaves annually) - After leaves fall, have dormant axillary buds with leaf scars below

Bundle scars mark food and water conducting tissue within leaf scars.

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