617 619 555 583 584 first step formation of the

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Unformatted text preview: d tissue Primary phloem Primary xylem Monocots Secondary Growth in Woody Stems Chapter 26 • • • Diameter growth in existing organs. Conifers & many magnoliid & eudicot flowering plants. Similar in both roots & stems. Onset of Secondary Growth (p. 617-619; 555, 583-584) First Step: Formation of the vascular cambium. • Undifferentiated procambium between xylem & phloem. – Main source in basswood (Tillia)-type stems. • Pith ray Parenchyma. – Important in elderberry (Sambucus)-type stems. Cambium formation: elderberry-type stem. Cortex Pith ray 10 Vascular bundle Fascicular cambium Interfascicular cambium Once formed, V.C. periodically produces new layers of 20 xylem (inside) & 20 phloem (outside). Sequence of Primary & Secondary Stem Development: (See important chart on P. 635; 583) Ground meristem Protoderm Procambium 1) early primary tissue differentiation near apical meristem Primary & Secondary Stem Development Pith Cortex Pith ray 1o Xylem Procambium Epidermis 1o phloem 2) Mature primary stem tissues Primary & Secondary Stem Development Fascicular cambium Interfascicular cambium 3) Vascular cambium forms Primary & Secondary Stem Development Cork cambium Pith Cortex 2o phloem 1o Xylem 2o Xylem Epidermis Vascular cambium 1o phloem 4) First season of secondary growth Primary & Secondary Stem Development 2o phloem 2o Xylem (2 rings) Periderm Vascular cambium 5) Secondary growth continues: After 2 seasons Wood = Secondary Xylem Annual Rings: p. 632; 585 Annual 585 • spring wood: fast growth, large cells, light. • summer wood: slow growth, Small, dense cells, dark. summer Spring growth Summer growth Previous year’s growth Focus Plant 3: Wood; Pinus sp. (pines) 110 species mostly in temperate zone & mountainous areas of tropics. ½ all species native to Mexico, C. America, & Caribbean. Economically Important for timber & pulpwood. Driving force in historic development of E. TX economy. Major part of local economy today. East TX is sometimes called the “Pineywoods”. Historic logging of Pine in Texas Loblolly Pine in Texas Characteristics of Pine Woody plants: trees, shrubs. Evergreen, Needle-shaped leaves in bundles. Seeds borne on woody cones. pollen on separate pollen cones. Male (pollen) cones Female (ovulate, seed) cones The 3 Native Pines of East Texas Loblolly pine (Pinus taeda) medium-length needles medium cones Most widespread Most species today species Shortleaf pine Pinus echinata short (<4”) needles small cones Most common on Most drier, sandy sites drier, Longleaf pine Pinus palustris Long (>10”) needles Large cones More common More historically. historically. Monocot (Bamboo, Palm, Greenbriar) “Wood” Lignified woody tissue, but thickness all result of primary growth at & near apical meristem. Bamboo Greenbriar Fossilized palm “wood” Note scattered bundles Palm The Periderm (p. 619; 585) Originates: Cork cambium (=phellogen). Originates: Lenticils: areas of cork with airspaces...
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This document was uploaded on 03/28/2014 for the course BIO 131 at Stephen F Austin State University.

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