What is tigellum? Describe its parts.

Explanation

### Step-by-Step Solution:

1. **Definition of Tigellum**:
- Tigellum, also spelled as "Tegulum," is defined as the main axis of the embryo in seed plants. It serves as the central structure from which the root and shoot systems develop.

2. **Identification of Parts**:
- The Tigellum has two distinct ends, each responsible for the development of different plant structures:
- **Radical**:
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