What is placentation? Describe the various types of placentation in plants.

What is placentation? Describe the various types of placentation in plants. 
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Ans: It is arrangement of ovules in the ovary. Part of the ovary from which ovules arise is called as placenta. Placentation is of the following types.

I. Marginal placentation: Ovules are borne along the ventral suture of unilocular monocarpellary ovary. Ex: Dolichos

II. Parietal placentation: Ovules are borne on the inner surface of ovary wall where the margins of adjacent carpels are fused. Ex: Brassica, Cucurbita.

III. Axile placentaton: In this, the ovules are attached to a central axis present in the bilocular to multilocular ovary. Ex: Hibiscus

IV. Free central placentation: It is formed from axile placentation. It is fomed due to dissolution of septal walls which makes the ovary unilocular leaving free placental axis with ovules at the centre. Ex: Dianthus

V. Superficial placentation: Ovules arise all over the inner surface of each locule of multilocular ovary. Ex: Nymphaea

VI. Basal placentation: One or few ovules arise from the base of the unilocular ovary.

Ex: Tridax, Helianthus. 
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