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 1 4/5/2013 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. 2 4/5/2013 Organs: STEM DICOT MONOCOT Herbaceous Dicot Stems Have discrete vascular bundles arranged in a cylinder. 3 4/5/2013 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 4 4/5/2013 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. 5 4/5/2013 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 6 4/5/2013 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 7 4/5/2013 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. 8 4/5/2013 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. 9 .