Placenta are soft cushion like tissues with which the ovules are attached to the inner surface 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 the marginal of placenta grow in word and fuse, thus making a multilocular ovary, as in China rose, tomato, etc.

Parietal Placentation In this 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 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 a single ovule is attached to it, as in sunflower.

The process of shedding of leaves during hot summer or in autumn by deciduous plants is known as abscission. Anatomically, the cells of abscission zone are thin-walled and without deposition of lignin or suberin. At the time of abscission, the middle lamella may dissolve between the cells of two middle layers but the primary wall remain intact. The middle lamella as well as the primary walls of the adjacent cells is dissolved. Ultimately the whole cells of middle layer found in the abscission layer gets dissolve completely. Thus, there is separation of plant organ, i.e., leaf from the plant, wherever there is rainfall or wind.

Evergreen plant are those which has leaves persistent in all the four seasons. In contrast to deciduous plants which completely loose their foliage during winter or dry season. Pinus belonging to gymnosperms is an evergeen tree. The flowering plants under conditions of extreme cold shed their leaves and become dormant. But Pinus due to the presence of bark, which is thick, needle-like leaves having sunken stomata, reduce the rate of transpiration. The cold areas are both physiologically and physically dry due to scanty rainfall, precipitation as snow, decreased root absorption at low temperature and exposed habitats.

But, Pinus is well adapted to such conditions. It continues to manufacture food during this period and grown to dominate other plants. This show that Pinus is an evergreen tree. It do not shed its leaves, i.e., needles under any condition.

A. If a plant cell is cut in different plane if result, in radial symmetry.

B. If a plant cell is cut in two equal halves it result in bilateral symmetry.

These terms mean as listed

Structure	Function	Diagram
Plasmodesmata These are microscopic connecting channels between the two cells through the cell wall.	Allow communication and transport between two neighbouring cells. Plasmodesmata allow molecules to travel between plant cells through the symplastic pathway.
Middle lamella It is a layer in the cell wall mainly made of calcium pectate.	Performs the function of cementing between the two neighbouring cells.
Secondary wall It is a non-extensible layer made of hemicellulose fibres, in the cell wall of plant cells.	Provides rigidity to the cell wall in plant cell.