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Thickening of older woody stems thickening roots

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Unformatted text preview: Phloem Differentiation, Time Secondary Growth in Plants Woody plants (trees & shrubs). Thickening of older, woody stems & Thickening roots. roots. Only in preexisting plant parts. Only in 2 secondary meristems involved: Vascular cambium: adds new woody layer to stem each season. Cork cambium forms outer covering (periderm) & epidermis. Cells & Tissues of the Plant Body Parenchyma Cells: (p. 541; 513-514) 513-514) • Often in continuous masses Often (Parenchyma tissue). (Parenchyma • Living at maturity. • Only a primary cell wall. • Basic metabolism, photosynthesis, Basic storage, secretion & transport. storage, • Most numerous cell type • Retain ability to divide & originate new Retain meristems 'totipotent'. meristems Transfer Cells (p. 542; 514) Parenchyma cells with wall ingrowths to increase membrane surface area. membrane High-volume short-distance solute movement Often adjacent to vascular tissues, etc. Collenchyma Cells (p. 542-543; 514) Unevenly thickened non-lignified, flexible cell walls. cell Support soft, growing tissues. Living at maturity. Occur as strands of collenchyma tissue. Occur collenchyma • “Strings” in celery. Sclerenchyma Cells (p. 543-544; 514-516) Mechanical cells: hard, rigid secondary cell wall, dead at Mechanical maturity. – Sclerids: short branched; fruits, nuts, etc. – Fibers: long, in strands; mature parts of all plants. Occur both in-mass (sclerenchyma tissue) & mixed with other cell types. other Fibers Sclerids Xylem: (p. 544-546; 516-518) (Part 1 of the Vascular tissue system) Conducts water & soil minerals. Mechanical support. Two possible origins: • root & shoot apical meristem (primary growth) = root primary xylem. primary • From vascular cambium (secondary growth) = From secondary xylem = wood. secondary Complex tissue (many cell types). Types of Cells in xylem: (p. 544-545; 517-518; chart p. 548; 519) Tracheids: Tracheids: • Small diameter conducting cells • All vascular plant groups. Vessel members: • Larger diameter, flat perforated ends. • Flowering plants only. Parenchyma --storage. Sclerenchyma fibers: strength. Tracheid Vessel Phloem (p. 546-553; 519-523) Principal food conducting tissue of vascular plants: Principal • Transports sugars (sucrose). • Other substances: Amino acids, hormones, lipids, Other nutrients etc. nutrients Two origins: Primary Phloem. Secondary phloem. Complex tissue: more than 1 cell type. Phloem Cell Types (p. 543; 519 (Table 23-1) Sieve elements-- Conducting cells: Living cytoplasm but no nucleus Living • Sieve cells (gymnosperms). • Sieve tube members (have sieve Sieve plates), flowering plants. Specialized parenchyma helper cells: • Albuminous cells (gymnosperms). • Companion cells (flowering plants). Other parenchyma cells. Sclerids & fibers. Sieve tube Companion cell Dermal Tissues: Epidermis (p. 553-555; 523) Covers/ protects non-woody plant parts. Covers/ Origin: apical meristems (primary...
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