Endothecium and tapetum in anther are derived from primary parietal layer. Let's understand the formation of anther and the origin of its different layers.

Formation of Anther
Anther is a part of the stamen, which is the male reproductive organ of a flower. It consists of two lobes, each containing two microsporangia or pollen sacs. The anther is surrounded by four layers of cells, which are:

1. Epidermis
2. Endothecium
3. Middle layer
4. Tapetum

Origin of Different Layers
The four layers of cells in the anther are derived from two different layers of cells in the developing flower bud. They are:

1. Primary sporogenous layer: It is the innermost layer of cells in the developing flower bud. It gives rise to the microsporocytes or pollen mother cells, which undergo meiosis to form haploid microspores that develop into pollen grains.

2. Primary parietal layer: It is the outermost layer of cells in the developing flower bud. It gives rise to the different layers of cells in the anther, as described below:

- Epidermis: It is derived from the outermost layer of the primary parietal layer.
- Endothecium: It is derived from the innermost layer of the primary parietal layer. It forms the inner layer of the anther wall and helps in dehiscence (opening) of the anther to release the pollen grains.
- Middle layer: It is derived from the middle layers of the primary parietal layer.
- Tapetum: It is derived from the innermost layer of the primary parietal layer. It is the most important layer of the anther, as it provides nourishment to the developing microspores and helps in their maturation. It also produces the enzymes and proteins that form the pollen coat.

Conclusion
Thus, the endothecium and tapetum in anther are derived from the primary parietal layer, which is the outermost layer of cells in the developing flower bud.

Primary parietal cells divide to form two layers of secondary parietal cells. The outer layer of secondary parietal cells differentiates to form endothecium and the inner layer of secondary parietal cells divide to form two layers, one of which forms the middle layers and the other forms the tapetum.