Lecture 4

Lecture 4 - Lecture 4 1/31/08 1 Last time: Cell types:...

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Lecture 4 1/31/08 1 Last time: Cell types: Epidermis, parenchyma, collenchyma, sclerenchyma, vascular tissues: primary phloem, primary xylem I. Xylem tissue (4 types of cells) -- function: conduction of water A. review 1. PARENCHYMA 2. FIBERS 3. XYLARY (=tracheary) ELEMENTS: the water conducting cells a. dead at maturity b. thick secondary wall thickenings inside primary wall B. two types of xylary elements: (study page 719) 1. tracheids --long and thin with slanted, pitted end walls --water moves from tracheid to tracheid through PITS. 2. vessel elements --shorter and wider; PITS on lateral walls --open perforations on end walls: no primary CW present Vessel elements stacked end to end are called a vessel. Water flows through perforation plates from vessel element to vessel element within a vessel. Eventually some vessel elements will have end walls. Then water must exit that vessel and move into another. Lateral walls on both tracheids and vessels can vary from annular to pitted.
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Lecture 4 1/31/08 2 II. Concept of primary growth A. Primary growth results from shoot and root apical meristems (primary meristems), including axillary buds. Remember: meristem--region of rapidly dividing cells; plants have other meristems in addition to shoot and root apical meristems. B. PRIMARY GROWTH: GROWTH IN LENGTH C. Primary growth is responsible for the non-woody, or herbaceous, part of the plant body. However, many plants grow in girth as well as in height. III. Secondary Growth (=lateral growth==>wood and bark) A. Concept of secondary growth (=cambia): 1. Secondary growth == Lateral growth that occurs most commonly via lateral meristems= cambiums ==meristems that produce cells to the inside and outside along the longitudinal axis. 2.
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Lecture 4 - Lecture 4 1/31/08 1 Last time: Cell types:...

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