What is placentation? What are the different types of placenta seen in plants?
Placentation refers to the arrangement of ovules within the ovary. Ovules are attached to ovarian walls through special structures called as placenta. Placentation can be marginal, axile, parietal, basal, free central or superficial in position.
Marginal placentation: It is seen in the pea seed. The placentation occurs as a ventral suture of the ovary. Ovules are arranged in two rows along the margins of the ovary.
Axile placentation: It is seen in tomato seed. Placenta is axial and the ovules are formed at the angles where the septa join the central placenta. Ovules placed along the central axis of the ovary.
Parietal placentation: It is seen in mustard seed. In this type of placentation, the ovules develop on the periphery of the ovary. Ovary has a single chamber but appears to be double-chambered because of the formation of a false septum.
Basal placentation: It is seen sunflower. There occurs one ovule attached at the base.
Free central placentation: It is seen in primrose. Ovules lie on the central axis.
Superficial placentation: It is seen in nymphea. Ovules are almost attached entirely to the inner surface of the ovary.