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Tuesday, 31 January 2017

Anatomy of flowering plants II










Epidermal Tissue System
  • It forms the outermost covering of whole plant body, which consists of epidermal cells, stomata, epidermal appendages (trichomes and hairs).
  • Epidermis is single layered, parenchymatous with waxy thick layers of cuticle to prevent water loss.
  • Stomata is present in epidermis of leaves. It regulates the transpiration and gaseous exchange. In dicots, stomata are bean-shaped having two guard cells closing the stomatal pore. In monocots, stoma is dumbbell-shaped. Guard cells contain chloroplasts that help in opening and closing of stomata.
  • Epidermis also contains a number of hairs. Root hairs are unicellular elongation of epidermal cells. Trichomes are present on stems, which are multicellular, branched or un-branched preventing water loss due to transpiration.
The ground Tissue System
  • All the tissue between epidermis and vascular bundle forms the ground tissues. It consists of simple permanent tissues. Parenchyma is present in pericycle, cortex, pith and medullary rays in stem and roots.
  • Leaves the mesophyll, chloroplast containing cell forms the ground tissues.

The Vascular Tissue System
  • The vascular system consists of complex tissues, xylem and phloem that together form vascular bundles.
  • When xylem and phloem within a vascular bundle are arranged in alternate manner on different radii, the arrangement are called radial as in roots. When xylem and phloem are situated at the same radius of vascular bundle, it is called conjoint as in stem and leaves.
Dicotyledonous Root
  • The outermost layer of dicots root is epidermis containing unicellular root hairs. Below epidermis is the many cell thick parenchymatous cells with intercellular spaces.
  • The innermost layer of cortex is called endodermis having waxy material suberin as casparian strips, which is impermeable to water.
  • Pericycle is present below endodermis. The parenchymatous cells lying between xylem and phloem are called conjuctive tissue.
  • Two to four xylem and phloem patches are present. All the tissues inside the endodermis constitute the stele
Monocotyledonous Roots
Anatomically monocots roots epidermis cortex, endodermis, pith are similar to dicots except having more than 6 vascular bundles with larger pith.

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