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Chapter 29.6

Chapter 29.6. Accumulated Secondary Growth The Woody Plants. AP Biology Spring 2011. Secondary Growth. Secondary growth: increases the circumference of woody plants Some monocots, many eudicots, magnoliids, and most gymnosperms add secondary growth Woody plants! . Secondary Growth.

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Chapter 29.6

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  1. Chapter 29.6 Accumulated Secondary Growth The Woody Plants AP Biology Spring 2011

  2. Secondary Growth • Secondary growth: increases the circumference of woody plants • Some monocots, many eudicots, magnoliids, and most gymnosperms add secondary growth • Woody plants!

  3. Secondary Growth • Differences emerge as their lateral meristems become active • Meristems produce secondary xylem and phloem • Vascular Cambium: consists of two types of cells • Long narrow cells increase the height of stem • Small rounded cells produce rays that increase the stems circumference

  4. Secondary Growth • Vascular Cambium: • Secondary xylem forms on inner face of meristem • Secondary phloem forms on outer face of meristem

  5. Secondary Growth • In spring, primary growth resumes at the stem’s buds, secondary growth is added inside it • Vascular cambium is like a cylinder, one or a few cells thick • Some cells (fusiform initials) give rise to secondary xylem and phloem that extend lengthwise through the stem • Other cells (ray initials) form horizontal rays of parenchyma, in a pattern similar to spokes of bike wheel

  6. Secondary Growth • Page 504 • Figure 29.20

  7. Woody Roots • Secondary xylem and phloem also form at vascular cambium in the plant’s roots • Page 505, figure 29.22

  8. Woody Vs. Non-woody Plants • Woody stems and roots have advantages: • Plants with taller stems or broader canopies intercept more energy streaming in from the sun • By acquiring more energy for photosynthesis, they have the metabolic means to form large root and shoot systems • This allows them to be more competitive

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