Question

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

Answer 1

Placentation: The arrangement of ovules within the ovary is known as placentation. The placentation is of different types namely, marginal, axile, parietal, basal, central and free central. In 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, as in pea. When the placenta is axial and the ovules are attached to it in a multilocular ovary, the placentation is said to be axile, as in china rose, tomato and lemon. In parietal placentation, the ovules develop on the inner wall of the ovary or on the peripheral part. The ovary is one-chambered but it becomes two-chambered due to the formation of the false septum, e.g., mustard and Argemone. When the ovules are borne on a central axis and septa are absent, as in Dianthus and Primrose the placentation is called free central. In basal placentation, the placenta develops at the base of the ovary and a single ovule is attached to it, as in sunflower or marigold.

Marginal

Parietal

Axile

Free central

Basal