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Tuesday, 31 January 2017

Anatomy of Flowering Plants I

Anatomy is the study of internal structure of organism. In plants anatomy includes histology, that is, organization and structure of tissues. Anatomy helps in knowing the structural peculiarities of different group of plants and indicates the structural adaptation to diverse environments.

The tissue
A group of cells having a common origin and usually performing common function are called tissues.

  • A meristem or meristematic tissue is a simple tissue composed of a group of similar and immature cells which can divide and form new cells. The meristem which occurs at tips of roots and shoots and produce primary tissues are called apical meristem.
  • Intercalary meristem occurs between mature tissues especially in grasses. It is also primary tissue. The meristem occurs on the sides and takes part in increasing girth of the plants are called Lateral meristem. Intrafascicular cambium in the primary lateral meristem. Vascular cambium, cork cambium are secondary meristem.
  • The cells that have become structurally and functionally specialized and lose the ability of cells division are called permanent tissue. Permanent tissues having all cells similar in structure and function are called simple permanent tissues and those having different kinds of cells are called complex tissue.
Parenchyma is a simple permanent living tissue which is made up thin-walled similar isodiametric cells. Each cell encloses a large central vacuole and peripheral cytoplasm containing nucleus. They are found in non-woody and soft areas of stem, root, leaves, fruits and flowers. They store the food and provide turgidity to softer parts of plant.

Collenchyma consists of cells which are much thickened at corner due to cellulose, hemicellulose and pactin. Oval, spherical or polygonal often contain chlorophyll. They provide mechanical support to the growing parts of the plants like young stem.

Sclerenchymas are supportive tissue having highly thick walled cells with little or no protoplasm due to deposition of cellulose or lignin. They are of two types fibres and sclereids. Mechanical support to mature plant organs to tolerate bending, shearing, compression etc.
Complex Tissues – Xylem and phloem constitute the complex tissues in plants and work together as a unit.
  • Primary xylem is of two types- protoxylem and mataxylem. In stem, protoxylem lies in centre and mataxylem towards periphery. This type of primary xylem is called endarch.
  • In roots, protoxylem lies in periphery and metaxylem lies towards the centre. This type of primary xylem is called exarch.
  • In gymnosperms, albuminous cells and sieve cells, they lack sieve tube and companion cells.
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