What is true of wall of pollen sac

Options

A. Endothecium occurs inner to tapetum
B. Tapetum lies below the endothecium
C. Middle layers occur below the epidermis and outside the tapetum
D. Middle layers lie between endothecium and tapetum.

Answer

### Step-by-Step Solution:

1. **Understanding the Structure of the Pollen Sac Wall**:
The wall of the pollen sac is composed of four distinct layers. These layers are arranged in a specific order from the outermost to the innermost.

2. **Identifying the Layers**:
- **Epidermis**: This is the outermost layer of the pollen sac.
- **Endothecium**: This layer is located just beneath the epidermis and consists of a single layer of cells.
- **Middle Layers**: These consist of 2-3 layers of cells and are situated below the endothecium.
- **Tapetum**: This is the innermost layer that surrounds the sporogenous tissue completely.

3. **Order of Layers**:
The correct order of the layers from outside to inside is:
- Epidermis
- Endothecium
- Middle Layers
- Tapetum

4. **Analyzing the Options**:
- **Endothecium occurs in there to tapetum**: This is incorrect because the endothecium is not inside the tapetum.
- **Tapetum lies below the endothelium**: This is also incorrect as the tapetum is the innermost layer, which means it lies below the middle layers, not the endothecium.
- **Middle layers occur below the epidermis and outside the tapetum**: This statement is incorrect as the middle layers are located between the endothecium and the tapetum.
- **Middle layers lie between the endothelium and tapetum**: This is the correct statement as it accurately describes the position of the middle layers.

5. **Conclusion**:
The correct answer is that the middle layers lie between the endothelium and tapetum.