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Biology LibreTexts

11: Secondary Growth

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  • Learning Objectives

    Content Objectives

    • Learn the sequence of development of meristems and tissues in secondary growth
    • Understand the tradeoffs (costs and benefits) of secondary growth

    Skill Objectives

    • Identify anatomical features of woody stems
    • Determine the age of a tree based on annual growth rings

    • 11.1: Formative Questions
    • 11.2: Introduction
      In secondary growth, primary tissues and residual meristematic tissues produce secondary meristems, which then produce secondary tissues. Whereas primary tissues allow for vertical growth, secondary tissues allow for lateral growth: they allow stems and roots to become wider.
    • 11.3: Secondary Tissues in the Root
      In roots, the formation of both secondary meristems involves the pericycle. The pericycle and some residual procambium join together to form the vascular cambium, a secondary meristem that produces vascular tissue. The other secondary meristem, the cork cambium, is initially formed solely from the pericycle. Each of these secondary meristems divides in two directions to form a different secondary tissue to the inside and outside of the meristematic layer, respective to the center of the plant.
    • 11.4: Flowcharts of Development
    • 11.5: Secondary Tissues in the Shoot
      Though the secondary tissues are all the same, the sequence of secondary meristem development in shoots is a bit different than in roots. Shoots have no pericycle, so the secondary meristems must be formed from different tissues. In shoots, the vascular cambium is formed from residual procambium within the vascular bundles (fascicular cambium) joined by tissue in the pith rays (interfascicular cambium).
    • 11.6: Dendrochronology
      Dendrochronology is a process used to determine the order and timing (chronology) of events using information in tree rings (dendro- refers to trees). These rings form in response to environmental conditions, storing information on climate and historic occurrence of fires in an area. Essentially, you bore a hole into a living tree and extract a thin section column of the wood. This becomes your reference specimen, as you date each annual ring, tracing back from the present date.
    • 11.7: Summative Questions

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