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Tuesday, 31 January 2017

Morphology of Flowering Plants II

The Leaf
  • Leaf is a green, dissimilar exogenous lateral flattened outgrowth which is borne on the node of a stem or its branches is specialized to perform photosynthesis
  • Leaves originate from shoot apical meristem and are arranged in an acropetal order.
  • A typical leaf consists of three parts: Leaf base, Petiole, Lamina. Leaf is attached with stem by Leaf Base which may bear two small leaf like structure called stipule.
  • Middle prominent vein is called mid vein. Veins provide rigidity to the leaf blade and act as channel for transport of water and minerals.
  • The arrangement of vein and veinlets in the lamina is called venation.

  • A leaf having a single or undivided lamina is called Simple leaf. The incisions do not touch the mid rib. Example- Mango, Guava etc.
  • When the incision of lamina reach up to the midrib and breaking it into a number of leaflets called Compound leaves.
  • In a Pinnately compound leaves, a number of leaflets are present on common axis called rachis. Example: Neem.
  • In Palmately compound leaves, the leaflets are attached at common point. Example-Silk cotton.
  • The pattern of arrangement of leaves on the stem or branch is called Phyllotaxy.
  • In alternate type of phyllotaxy single leaf arise at each node as in China rose.
  • In opposite types of phyllotaxy a pair of leaves arise from each node opposite to each other as in Guava.
  • If more than two leaves arise at a node and form a whorl is called whorled type of phyllotaxy as in Alastonia.
  • Leaves are modified to perform other function like converted to tendril for climbing as in Peas and spines for defence in Cactus.
The arrangement of flowers on the floral axis is termed as inflorescence. Two main types of inflorescence are racemose and cymose

The flower
  • Flower is the reproductive part of angiospermic plants for sexual means of reproduction. A typical flower has four whorls arranged on a swollen end of stalk or pedicel called thalamus. They are Calyx, Corolla, Androecium and Gynoecium.
  • When a flower have both androecium and gynoecium, the flower is called bisexual and flower having either androecium or gynoecium only is called unisexual.
  • When flower can be divided into two equal radial halves in any radii passing through center the symmetry of flower is called actinomorphic (radical symmetry) as in Mustard, Datura, and Chili.
  • When flower can be divided into two similar parts only in one vertical plane it is zygomorphic as in Pea, Gulmohar, Cassia etc.
  • Floral appendages are in multiple of 3,4 or 5 they are called trimerous, tetramerous and pentrmerous respectively. Flower with reduced small leaf at the base of pedicel are called bracteates and without it ebrateate.
  • Based on the position of ovary with respect to other floral part on thalamus flowers are of following types
a. Hypogynous flower Ovary occupies the highest position. The ovary in such case is called superior. Eg. Mustard, brinjal and china rose.
b. Perigynous flowers If the gynoecium is situated at the centre and other parts are on the rim at same height. Ovary is called half-inferior.
c. Epigynous flowers The margin of thalamus grows to completely cover the ovary. Ovary is said to be inferior.

Calyx is the outermost whorls of the flower; its members are called sepals. They are generally green and leafy; protect the flower in bud stage. It may be gamosepalous (sepals united) or polysepalous (sepals free).

Corolla consists of petals, brightly coloured to attract the insects for pollination. They may be gamopetalous or polypetalous.

The mode of arrangement of sepals or petals in floral bud with respect to the other members of same whorl is called aestivation. In valvate, the whorls of sepals or petals touch each other as in Calotropis. In Twisted aestivation, the whorls overlap each other as in China rose.
In Imbricate aestivation, margin overlap each other but not in particular fashion as in Gulmohur. In Vaxillary aestivation, in five petals largest overlap the other two laterally and in turn two smaller are overlapped by the two above as in Pea and Bean flowers.

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