Dicot root-Anatomy.pptxghhbbjjbhjjnjjjjh

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1. Dicot root- Anatomy

2. Anatomy of Dicot root Epiblema Cortex Endodermis Pericycle Vascular bundles Pith

3. Epiblema or Epidermis  - It is the outermost unilayered with several unicellular root hairs. It consists of thin walled, compactly arranged living parenchymatous cells. Usually epiblema is characterised by absence of stomata and cuticle. Sometimes the epiblema may be less cuticularised . It provides protection to the roots due to presence of unicellular root hairs it also helps in absorption of water and minerals from soil.

4. 3. Endodermis -  It is the innermost layer of cortex and covers the stele. It consists of compactly arranged barrel shaped parenchyma without intercellular spaces. Most of the cells are characterised by the presence of special thickening of suberin and lignin on their radial and tangential walls called  casparian strips . Some endodermal cell near protoxylem has no casparian strips and called  passage cells  or transfusion cells. These cells allow radial diffusion of water and minerals through the endodermis.

5. Pericycle -  It is the outermost layer of stele and composed of uniseriate layer of parenchymatous cells without intercellular spaces. Some dicots and hydrophytes do not bear pericycle . Several lateral roots and lateral meristem arise from pericycle region (hence lateral roots are endogenous in origin). At the time of secondary growth, it produces secondary cambium or phellogens .

6. Vascular bundles -  They are 2-8 in number, radial and arranged in ring. Xylem and phloem bundles are separated from each other by parenchymatous  cells called conjuctive or  complementary tissue . Xylem  is exarch (i.e. protoxylem towards the periphery and metaxylem towards the centre) and consists of tracheids , vessels, xylem parenchyma and xylem fibres . The  pholem   forms oval masses beneath the pericycle , alternating with xylem bundles. Pholem consists of sieve tubes, companion cells and pholem parenchyma. Usually pholem fibres are absent or reduced.

7. Distinguishing Features of Dicot Root      The typical  dicot  roots show following features. Epiblema   is  uniseriate , thin walled,  colourless  without intercellular spaces and produce unicellular root hairs, hence also called as  piliferous  layer or  rhidodermis . Cortex  is homogenous (without differentiation). Endodermis  consists of barrel shaped compact  parenchymatous  cells. It contains both  casparian  stripes and passage cells. Pericycle   uniseriate  and become  meristematic  to give secondary roots and secondary tissues. Vascular  bundles are radial; Xylem is  exarch , number of xylem bundles varies from 2 to 4 rarely more ( upto  6-8).  Metaxylems  are angular arranged in linear. Usually  conjuctive  tissues  are well developed. Pith  is very small or completed obliterated.

8. Secondary growth

9. The vascular cambium is completely secondary in origin. It originates from a combination of conjunctive tissue located just below the phloem bundles, and as a portion of pericycle tissue present above the protoxylem to form a complete and continuous wavy ring. This wavy ring later becomes circular and produces secondary xylem and secondary phloem similar to the secondary growth in stems.

10. Origin of Lateral Roots The lateral roots are endogenous in origin (from a deeper layer). The seat of its origin is cells of pericycle , usually opposite a protoxylem group, become meristematic and go on dividing periclinally and anticlinally . Lateral Root showing the Vascular Connection between it and the parent Stele. Lateral roots are produced in a definite pattern. The youngest roots are closing (proximal) to the apex.

11. The pattern of lateral root production is readily observed with tap root systems. The tap root can also be called the primary root while its branches are called secondary or lateral roots. The origin of lateral roots can be unraveled for species that have fibrous root systems. The hump penetrates into the cortex, and emerges as a lateral branch.

12. Later, the hump differentiates into 3 regions of the root apexdermatogen , Periblem and Plerome . Finally the lateral root comes out. The number of lateral roots corresponds to the number of xylem bundles.