Stem

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STEMSTEMOntogenetic developmentArrangement of Primary tissues

Ontogenetic developmentOntogenetic development

Types of stemA. aerialB. sub-aerialC. underground

Nature of stem/ TextureA. herbaceousB. woody

Arrangement of primary tissuesArrangement of primary tissues1. Epidermis2. Cortex3. Endodermis4. Stele

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CortexCortex

Parenchyma (photosyn., storage)CollenchymaFibersLacunateLacunateSclereids, laticifers, secretory cells

EndodermisEndodermis

Delimits the cortex from the vascular cylinderNot usually developed in stemsConspicuous in vascular cryptogamsConspicuous in vascular cryptogams+ Lignin and suberin along radial and transverse walls Maturation: suberin lamellae on the entire inner surface of the walls + cellulose + lignin

Starch sheathStarch sheath

Young eudicot stemsHomologous to endodermis

Primary vascular systemPrimary vascular system

Vascular bundle Continous

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Vascular bundleVascular bundle

collateral bicollateral

Vascular bundleVascular bundle

CONCENTRIC

Amphivasal-- some monocots-- Aloe, Agavaceae

Amphicribral-- Pteridophytes

Vascular bundleVascular bundle

Closed- without vascular cambiumOpen

With vascular cambium- With vascular cambium

SteleSteleAnything inside the endodermisPericycle + vascular tissues + pith

Anomalous structuresAnomalous structures

Medullary bundlesCortical bundles

Types of steleTypes of stele

Illustrates various stages of evolution of primary vascular system

A ProtosteleA. ProtosteleB. Siphonostele

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ProtosteleProtostele

Haplostele – SelaginellaActinostele – PsilotumPlectostele – Lycopodium

SiphonosteleSiphonostele-- advanced advanced PteridophytaPteridophyta and and SpermatophytaSpermatophyta

EctophloicAmphiphloic

Solenostele

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Overlapping leaf gapsOverlapping leaf gaps

Dictyostele--meristeles

Eustele

What type of bundle?

Atactostele

MedullaryMedullary raysrays

Not all interruptions are leaf gapsSome result from reduction of vascular tissue and formation of interfascicularparenchymapa e c y a

Primary xylem differentiationPrimary xylem differentiation

Endarch – differentation of metaxylemproceeds progressively towards the periphery (centrifugal– order of maturation))ExarchMesarchHow about the phloem?

Anatomy of the nodeAnatomy of the node

Leaf traceLeaf gap = “lacuna”

Classification (no of leaf gaps/leaf)Classification (no. of leaf gaps/leaf)1. Unilacunar2. Trilacunar -- primitive3. Multilacunar

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Axile bundle/ cauline bundleLeaf traceBranch trace

Vascular system of monocotsVascular system of monocots