Pit membrane of simple pit is formed by the middle lamella.

The pit membrane is a structure that connects adjacent cells in the xylem and allows for the movement of water and nutrients between them. It is formed by the middle lamella, which is a layer of pectin and other polysaccharides that holds adjacent cell walls together.

Explanation:

1. Structure of the pit membrane:
The pit membrane is a thin, perforated structure that separates two adjacent cells in the xylem. It is composed of the middle lamella, which is the layer of material that cements the primary cell walls of adjacent cells together. The middle lamella is primarily made up of pectin, a complex polysaccharide.

2. Function of the pit membrane:
The primary function of the pit membrane is to allow for the movement of water and nutrients between adjacent cells in the xylem. It is through these pits that water can move laterally from one cell to another, facilitating the transport of water and dissolved solutes throughout the plant.

3. Formation of the pit membrane:
The pit membrane is formed during cell wall development. When new cells are formed, the middle lamella is secreted between the adjacent cells, acting as a glue to hold them together. As the cells mature, the middle lamella becomes more rigid and forms the pit membrane.

4. Types of pits:
There are two types of pits: simple pits and bordered pits. Simple pits have a pit membrane that is only present on one cell wall, while bordered pits have a pit membrane that is present on both cell walls. In both cases, the pit membrane is formed by the middle lamella.

Conclusion:
In conclusion, the pit membrane of a simple pit is formed by the middle lamella. The middle lamella is a layer of pectin and other polysaccharides that holds adjacent cell walls together. The pit membrane allows for the movement of water and nutrients between adjacent cells in the xylem.