These are the densely stained reticular stuctures present near the nucleus, consisting of many flat, disc shaped cistemae of `0.5 - 1.0 mu m` diameter. These are

Options

A. chloroplasts
B. endoplasmic reticulum
C. mitochondria
D. Golgi apparatus

Explanation

To answer the question regarding the densely stained reticular structures near the nucleus consisting of flat, disc-shaped cisternae of 0.5 to 1.0 micrometer diameter, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics**: The question describes structures that are densely stained, reticular, and located near the nucleus. They consist of flat, disc-shaped cisternae with a specific size range of 0.5 to 1.0 micrometers.

2. **Analyze the Options**:
- **Chloroplast**: This organelle is involved in photosynthesis and is typically not described as having flat, disc-shaped cisternae. It is also not primarily located near the nucleus.
- **Endoplasmic Reticulum (ER)**: The ER is a network of membranes involved in protein and lipid synthesis. It does have a reticular structure but is not specifically described as having flat, disc-shaped cisternae.
- **Mitochondria**: These are known for their role in energy production and have a double membrane structure with inner folds called cristae, not flat cisternae.
- **Golgi Apparatus**: This organelle is known for processing and packaging proteins and lipids. It consists of stacked, flattened membrane-bound sacs called cisternae, which match the description provided in the question.

3. **Conclusion**: Based on the analysis, the structure that fits the description of densely stained reticular structures near the nucleus with flat, disc-shaped cisternae is the **Golgi apparatus**.

### Final Answer:
These are the **Golgi apparatus**.

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