Stem

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Stem

  1. 1. 2/17/2010 Ontogenetic development STEM Ontogenetic development Arrangement of Primary tissues Types of stem Arrangement of primary tissues A. aerial 1. Epidermis 2. Cortex B. sub-aerial 3. Endodermis C. underground 4. Stele Nature of stem/ Texture A. herbaceous B. woody 1
  2. 2. 2/17/2010 Cortex Endodermis Parenchyma (photosyn., storage) Delimits the cortex from the vascular Collenchyma cylinder Fibers Not usually developed in stems Lacunate Conspicuous in vascular cryptogams Sclereids, laticifers, secretory cells + Lignin and suberin along radial and transverse walls Maturation: suberin lamellae on the entire inner surface of the walls + cellulose + lignin Starch sheath Primary vascular system Young eudicot stems Homologous to endodermis Vascular bundle Continous 2
  3. 3. 2/17/2010 Vascular bundle Vascular bundle Amphivasal Amphicribral -- some monocots -- Pteridophytes collateral bicollateral -- Aloe, Agavaceae CONCENTRIC Vascular bundle Stele Closed Anything inside the endodermis - without vascular cambium Pericycle + vascular tissues + pith Open - With vascular cambium Anomalous structures Types of stele Medullary bundles Illustrates various stages of evolution of Cortical bundles primary vascular system A. A Protostele B. Siphonostele 3
  4. 4. 2/17/2010 Protostele Siphonostele- Siphonostele- advanced Pteridophyta and Spermatophyta Haplostele – Selaginella Actinostele – Psilotum Plectostele – Lycopodium Ectophloic Amphiphloic Solenostele 4
  5. 5. 2/17/2010 Overlapping leaf gaps Dictyostele Eustele Atactostele --meristeles What type of bundle? Medullary rays Primary xylem differentiation Not all interruptions are leaf gaps Endarch – differentation of metaxylem Some result from reduction of vascular proceeds progressively towards the tissue and formation of interfascicular periphery (centrifugal– order of pa e c y a parenchyma maturation)) Exarch Mesarch How about the phloem? Anatomy of the node Leaf trace Leaf gap = “lacuna” Classification (no. of leaf gaps/leaf) (no 1. Unilacunar 2. Trilacunar -- primitive 3. Multilacunar 5
  6. 6. 2/17/2010 Axile bundle/ cauline bundle Leaf trace Vascular system of monocots Branch trace 6

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