Question

The arrangements of ovules within the ovary is known as placentation. What does the term placenta refer to? Name and draw various types of placentations in the flower as seen in T.S. or V.S.

Answer 1

Placenta

Placenta is a tissue that arises from the wall of the ovary to which the ovules are attached to.

Types of placentation​

The arrangement of ovules within the ovary is known as placentation. The placentation are of different types: Marginal, axile, parietal, basal and free central.

Marginal placentation

Marginal placentation is the type of placentation in which ovules are present along the margins of the carpel along the ventral suture. It is found in monocarpellary and unilocular ovaries. Example: Pea.


Axile placentation
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Axile placentation is the type of placentation characterised by the presence of ovules at or near the centre, on the placenta, in each locule. It is seen in a bicarpellary or multicarpellary and multilocular ovary. Example: Tomato, lemon.


Parietal placentation

Parietal placentation is the type of placentation characterised by the presence of ovules on the periphery of the ovary wall. It is observed in bicarpellary or multicarpellary and unilocular ovary.
Example: Mustard, Argemone.


Free central placentation

Free central placentation is the type of placentation characterised by the presence of ovules on a central axis, the ovary is without any septa. It is seen in multicarpellary and unilocular ovaries.
Example: Dianthus, Primrose


Basal placentation

Basal placentation is the type of placentation characterised by the presence of ovules at the base of the ovary. It is found in bicarpellary or multicarpellary and unilocular ovary. The ovules are fewer or one. Example: Sunflower, marigold