question_answer 57)

  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 TS and VS.

Answer:

                  Placenta are soft cushion like tissues with which the ovules are attached to the innersurface of ovary wall. The arrangement of ovules within the ovary is known as placentation. The placentations are of different types, i.e., marginal, axile, parietal, basal and free central. Marginal Placentation In this 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. Axile Placentation In this placentation, the ovules are borne on central axis and themarginal of placenta grow in word and fuse, thus making a multilocular ovary, as in Chinarose, tomato, etc. Parietal Placentation In this placentation, the ovules develop on the inner wall of the ovaryor on peripheral part. Ovary is one chambered but it becomes two chambered due to theformation of a false septum known as replam, e.g., mustard. Free Central Placentation In this type of placentation, the ovules are present on the central axis of ovary and septa is absent so ovary is unilocular, as in Dianthus and Primose. Basal Placentation In this placentation, the placenta develops at the base of ovary and asingle ovule is attached to it, as in sunflower.