Morphology of Flowering Plants — BIOLOGY STD 11 Science — Question

Placenta is a parenchymatous cushion present inside the ovary where ovules are borne. The number, position, arrangement or distribution of placentae inside an ovary is called placentation. The placentations are of different types namely, marginal, axile, parietal, basal and free central.

1. Marginal placentation: The placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows, e.g., pea.
2. Axile placentation: When the placenta is axial and the ovules are attached to it in a multilocular ovary, the placentation is said to be axile, e.g., china rose, tomato and lemon.
3. Parietal placentation: The ovules develop on the inner wall of the ovary or on peripheral part. Ovary is one-chambered but it becomes two-chambered due to the formation of the false septum, e.g., mustard and Argemone
4. Free central placentation: When the ovules are borne on central axis and septa are absent, as in Dianthus and primrose the placentation is called free central.
5. Basal placentation: The placenta develops at the base of ovary and a single ovule is attached to it, as in sunflower, marigold.